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Several studies have demonstrated the potential for moderate, sustained weight loss to substantially reduce the risk for type 2 diabetes, regardless of whether weight loss was achieved by lifestyle changes alone or with adjunctive therapies such as medication or bariatricsurgery see energy balance section 1. About half the group lost more weight; half the group re-gained the weight they lost. Main cell types in blood. Both the quantity and the type or source of carbohydrates found in foods influence postprandial glucose levels. When stems of trees are subjected to wind, causing lateral stress, greater ethylene production occurs, resulting in thicker, more sturdy tree trunks and branches.
What is a food intolerance and what are the symptoms?
The glycemic loads of foods, meals, and diets are calculated by multiplying the glycemic index of the constituent foods by the amounts of carbohydrate in each food and then totaling the values for all foods. Foods with low glycemic indexes include oats, barley, bulgur, beans, lentils, legumes, pasta, pumpernickel coarse rye bread, apples, oranges, milk, yogurt, and ice cream. Fiber, fructose, lactose, and fat are dietary constituents that tend to lower glycemic response. Potential methodological problems with the glycemic index have been noted Several randomized clinical trials have reported that low—glycemic index diets reduce glycemia in diabetic subjects, but other clinical trials have not confirmed this effect Moreover, the variability in responses to specific carbohydrate-containing food is a concern Nevertheless, a recent meta-analysis of low—glycemic index diet trials in diabetic subjects showed that such diets produced a 0.
However, it appears that most individuals already consume a moderate—glycemic index diet 39 , Thus, it appears that in individuals consuming a high—glycemic index diet, low—glycemic index diets can produce a modest benefit in controlling postprandial hyperglycemia.
In diabetes management, it is important to match doses of insulin and insulin secretagogues to the carbohydrate content of meals. A variety of methods can be used to estimate the nutrient content of meals, including carbohydrate counting, the exchange system, and experience-based estimation.
By testing pre- and postprandial glucose, many individuals use experience to evaluate and achieve postprandial glucose goals with a variety of foods. To date, research has not demonstrated that one method of assessing the relationship between carbohydrate intake and blood glucose response is better than other methods.
Palatability, limited food choices, and gastrointestinal side effects are potential barriers to achieving such high-fiber intakes.
Substantial evidence from clinical studies demonstrates that dietary sucrose does not increase glycemia more than isocaloric amounts of starch 1. Thus, intake of sucrose and sucrose-containing foods by people with diabetes does not need to be restricted because of concern about aggravating hyperglycemia. Sucrose can be substituted for other carbohydrate sources in the meal plan or, if added to the meal plan, adequately covered with insulin or another glucose-lowering medication.
Additionally, intake of other nutrients ingested with sucrose, such as fat, need to be taken into account, and care should be taken to avoid excess energy intake. In individuals with diabetes, fructose produces a lower postprandial glucose response when it replaces sucrose or starch in the diet; however, this benefit is tempered by concern that fructose may adversely affect plasma lipids 1.
Therefore, the use of added fructose as a sweetening agent in the diabetic diet is not recommended. There is, however, no reason to recommend that people with diabetes avoid naturally occurring fructose in fruits, vegetables, and other foods.
Reduced calorie sweeteners approved by the FDA include sugar alcohols polyols such as erythritol, isomalt, lactitol, maltitol, mannitol, sorbitol, xylitol, tagatose, and hydrogenated starch hydrolysates.
Studies of subjects with and without diabetes have shown that sugar alcohols produce a lower postprandial glucose response than sucrose or glucose and have lower available energy 1.
When calculating carbohydrate content of foods containing sugar alcohols, subtraction of half the sugar alcohol grams from total carbohydrate grams is appropriate.
Use of sugar alcohols as sweeteners reduces the risk of dental caries. However, there is no evidence that the amounts of sugar alcohols likely to be consumed will reduce glycemia, energy intake, or weight. The use of sugar alcohols appears to be safe; however, they may cause diarrhea, especially in children.
The FDA has approved five nonnutritive sweeteners for use in the U. These are acesulfame potassium, aspartame, neotame, saccharin, and sucralose. Before being allowed on the market, all underwent rigorous scrutiny and were shown to be safe when consumed by the public, including people with diabetes and women during pregnancy.
Clinical studies involving subjects without diabetes provide no indication that nonnutritive sweeteners in foods will cause weight loss or weight gain It has been proposed that foods containing resistant starch starch physically enclosed within intact cell structures as in some legumes, starch granules as in raw potato, and retrograde amylose from plants modified by plant breeding to increase amylose content or high-amylose foods, such as specially formulated cornstarch, may modify postprandial glycemic response, prevent hypoglycemia, and reduce hyperglycemia.
However, there are no published long-term studies in subjects with diabetes to prove benefit from the use of resistant starch.
Two or more servings of fish per week with the exception of commercially fried fish filets provide n-3 polyunsaturated fatty acids and are recommended. The primary goal with respect to dietary fat in individuals with diabetes is to limit saturated fatty acids, trans fatty acids, and cholesterol intakes so as to reduce risk for CVD. Saturated and trans fatty acids are the principal dietary determinants of plasma LDL cholesterol.
In nondiabetic individuals, reducing saturated and trans fatty acids and cholesterol intakes decreases plasma total and LDL cholesterol. Reducing saturated fatty acids may also reduce HDL cholesterol. Studies in individuals with diabetes demonstrating the effects of specific percentages of dietary saturated and trans fatty acids and specific amounts of dietary cholesterol on plasma lipids are not available.
Therefore, because of a lack of specific information, it is recommended that the dietary goals for individuals with diabetes be the same as for individuals with preexisting CVD, since the two groups appear to have equivalent cardiovascular risk. In metabolic studies in which energy intake and weight are held constant, diets low in saturated fatty acids and high in either carbohydrate or cis -monounsaturated fatty acids lowered plasma LDL cholesterol equivalently 1 , However, high—monounsaturated fat diets have not been shown to improve fasting plasma glucose or A1C values.
In other studies, when energy intake was reduced, the adverse effects of high-carbohydrate diets were not observed 53 , Individual variability in response to high-carbohydrate diets suggests that the plasma triglyceride response to dietary modification should be monitored carefully, particularly in the absence of weight loss. Diets high in polyunsaturated fatty acids appear to have effects similar to monounsaturated fatty acids on plasma lipid concentrations 55 , 56 — Very-long-chain n-3 polyunsaturated fatty acid supplements have been shown to lower plasma triglyceride levels in individuals with type 2 diabetes who are hypertriglyceridemic.
Although the accompanying small rise in plasma LDL cholesterol is of concern, an increase in HDL cholesterol may offset this concern Glucose metabolism is not likely to be adversely affected. Very-long-chain n-3 polyunsaturated fatty acid studies in individuals with diabetes have primarily used fish oil supplements. In addition to providing n-3 fatty acids, fish frequently displace high—saturated fat—containing foods from the diet Two or more servings of fish per week with the exception of commercially fried fish filets 63 , 64 can be recommended.
Plant sterol and stanol esters block the intestinal absorption of dietary and biliary cholesterol. A wide range of foods and beverages are now available that contain plant sterols. If these products are used, they should displace, rather than be added to, the diet to avoid weight gain. Soft gel capsules containing plant sterols are also available.
In individuals with type 2 diabetes, ingested protein can increase insulin response without increasing plasma glucose concentrations. Therefore, protein should not be used to treat acute or prevent nighttime hypoglycemia.
High-protein diets are not recommended as a method for weight loss at this time. Although such diets may produce short-term weight loss and improved glycemia, it has not been established that these benefits are maintained long term, and long-term effects on kidney function for persons with diabetes are unknown. The RDA is 0. Good-quality protein sources are defined as having high PDCAAS protein digestibility—corrected amino acid scoring pattern scores and provide all nine indispensable amino acids.
Examples are meat, poultry, fish, eggs, milk, cheese, and soy. In meal planning, protein intake should be greater than 0. A number of studies in healthy individuals and in individuals with type 2 diabetes have demonstrated that glucose produced from ingested protein does not increase plasma glucose concentration but does produce increases in serum insulin responses 1 , Abnormalities in protein metabolism may be caused by insulin deficiency and insulin resistance; however, these are usually corrected with good blood glucose control However, the effects of high-protein diets on long-term regulation of energy intake, satiety, weight, and the ability of individuals to follow such diets long term have not been adequately studied.
Dietary protein and its relationships to hypoglycemia and nephropathy are addressed in later sections. Although numerous studies have attempted to identify the optimal mix of macronutrients for the diabetic diet, it is unlikely that one such combination of macronutrients exists. The best mix of carbohydrate, protein, and fat appears to vary depending on individual circumstances. For those individuals seeking guidance as to macronutrient distribution in healthy adults, the Dietary Reference Intakes DRIs may be helpful It must be clearly recognized that regardless of the macronutrient mix, total caloric intake must be appropriate to weight management goals.
Further, individualization of the macronutrient composition will depend on the metabolic status of the patient e. If adults with diabetes choose to use alcohol, daily intake should be limited to a moderate amount one drink per day or less for women and two drinks per day or less for men. To reduce risk of nocturnal hypoglycemia in individuals using insulin or insulin secretagogues, alcohol should be consumed with food.
In individuals with diabetes, moderate alcohol consumption when ingested alone has no acute effect on glucose and insulin concentrations but carbohydrate coingested with alcohol as in a mixed drink may raise blood glucose. Abstention from alcohol should be advised for people with a history of alcohol abuse or dependence, women during pregnancy, and people with medical problems such as liver disease, pancreatitis, advanced neuropathy, or severe hypertriglyceridemia.
If individuals choose to use alcohol, intake should be limited to a moderate amount less than one drink per day for adult women and less than two drinks per day for adult men. One alcohol containing beverage is defined as 12 oz beer, 5 oz wine, or 1. Moderate amounts of alcohol, when ingested with food, have minimal acute effects on plasma glucose and serum insulin concentrations However, carbohydrate coingested with alcohol may raise blood glucose.
For individuals using insulin or insulin secretagogues, alcohol should be consumed with food to avoid hypoglycemia. Evening consumption of alcohol may increase the risk of nocturnal and fasting hypoglycemia, particularly in individuals with type 1 diabetes Occasional use of alcoholic beverages should be considered an addition to the regular meal plan, and no food should be omitted.
Excessive amounts of alcohol three or more drinks per day , on a consistent basis, contributes to hyperglycemia In individuals with diabetes, light to moderate alcohol intake one to two drinks per day; 15—30 g alcohol is associated with a decreased risk of CVD The type of alcohol-containing beverage consumed does not appear to make a difference. There is no clear evidence of benefit from vitamin or mineral supplementation in people with diabetes compared with the general population who do not have underlying deficiencies.
Routine supplementation with antioxidants, such as vitamins E and C and carotene, is not advised because of lack of evidence of efficacy and concern related to long-term safety. Benefit from chromium supplementation in individuals with diabetes or obesity has not been clearly demonstrated and therefore can not be recommended. Uncontrolled diabetes is often associated with micronutrient deficiencies Individuals with diabetes should be aware of the importance of acquiring daily vitamin and mineral requirements from natural food sources and a balanced diet.
Health care providers should focus on nutrition counseling rather than micronutrient supplementation in order to reach metabolic control of their patients. Research including long-term trials is needed to assess the safety and potentially beneficial role of chromium, magnesium, and antioxidant supplements and other complementary therapies in the management of type 2 diabetes 71a , 71b.
In select groups such as the elderly, pregnant or lactating women, strict vegetarians, or those on calorie-restricted diets, a multivitamin supplement may be needed 1. Since diabetes may be a state of increased oxidative stress, there has been interest in antioxidant therapy.
Unfortunately, there are no studies examining the effects of dietary intervention on circulating levels of antioxidants and inflammatory biomarkers in diabetic volunteers.
The few small clinical studies involving diabetes and functional foods thought to have high antioxidant potential e. Clinical trial data not only indicate the lack of benefit with respect to glycemic control and progression of complications but also provide evidence of the potential harm of vitamin E, carotene, and other antioxidant supplements 1 , 72 , In addition, available data do not support the use of antioxidant supplements for CVD risk reduction Chromium, potassium, magnesium, and possibly zinc deficiency may aggravate carbohydrate intolerance.
Serum levels can readily detect the need for potassium or magnesium replacement, but detecting deficiency of zinc or chromium is more difficult In the late s, two randomized placebo-controlled studies in China found that chromium supplementation had beneficial effects on glycemia 76 — 78 , but the chromium status of the study populations was not evaluated either at baseline or following supplementation. Data from recent small studies indicate that chromium supplementation may have a role in the management of glucose intolerance, gestational diabetes mellitus GDM , and corticosteroid-induced diabetes 76 — However, other well-designed studies have failed to demonstrate any significant benefit of chromium supplementation in individuals with impaired glucose intolerance or type 2 diabetes 79 , Similarly, a meta-analysis of randomized controlled trials failed to demonstrate any benefit of chromium picolinate supplementation in reducing body weight The FDA concluded that although a small study suggested that chromium picolinate may reduce insulin resistance, the existence of such a relationship between chromium picolinate and either insulin resistance or type 2 diabetes was uncertain http: There is insufficient evidence to demonstrate efficacy of individual herbs and supplements in diabetes management In addition, commercially available products are not standardized and vary in the content of active ingredients.
Herbal preparations also have the potential to interact with other medications Therefore, it is important that health care providers be aware when patients with diabetes are using these products and look for unusual side effects and herb-drug or herb-herb interactions.
Individuals using rapid-acting insulin by injection or an insulin pump should adjust the meal and snack insulin doses based on the carbohydrate content of the meals and snacks.
For individuals using fixed daily insulin doses, carbohydrate intake on a day-to-day basis should be kept consistent with respect to time and amount. For planned exercise, insulin doses can be adjusted. For unplanned exercise, extra carbohydrate may be needed. The first nutrition priority for individuals requiring insulin therapy is to integrate an insulin regimen into their lifestyle. For individuals receiving basal-bolus insulin therapy, the total carbohydrate content of meals and snacks is the major determinant of bolus insulin doses Insulin-to-carbohydrate ratios can be used to adjust mealtime insulin doses.
Several methods can be used to estimate the nutrient content of meals, including carbohydrate counting, the exchange system, and experience-based estimation.
Improvement in A1C without a significant increase in severe hypoglycemia was demonstrated, as were positive effects on quality of life, satisfaction with treatment, and psychological well-being, even though increases in the number of insulin injections and blood glucose tests were necessary.
For planned exercise, reduction in insulin dosage is the preferred method to prevent hypoglycemia For unplanned exercise, intake of additional carbohydrate is usually needed. More carbohydrate is needed for intense activity. A American Diabetes Association statement addresses diabetes MNT for children and adolescents with type 1 diabetes Individuals with type 2 diabetes are encouraged to implement lifestyle modifications that reduce intakes of energy, saturated and trans fatty acids, cholesterol, and sodium and to increase physical activity in an effort to improve glycemia, dyslipidemia, and blood pressure.
Plasma glucose monitoring can be used to determine whether adjustments in foods and meals will be sufficient to achieve blood glucose goals or if medication s needs to be combined with MNT.
Healthy lifestyle nutrition recommendations for the general public are also appropriate for individuals with type 2 diabetes. Because many individuals with type 2 diabetes are overweight and insulin resistant, MNT should emphasize lifestyle changes that result in reduced energy intake and increased energy expenditure through physical activity. Because many individuals also have dyslipidemia and hypertension, reducing saturated and trans fatty acids, cholesterol, and sodium is often desirable.
Therefore, the first nutrition priority is to encourage individuals with type 2 diabetes to implement lifestyle strategies that will improve glycemia, dyslipidemia, and blood pressure. Although there are similarities to those above for type 1 diabetes, MNT recommendations for established type 2 diabetes differ in several aspects from both recommendations for type 1 diabetes and the prevention of diabetes.
MNT progresses from prevention of overweight and obesity, to improving insulin resistance and preventing or delaying the onset of diabetes, and to contributing to improved metabolic control in those with diabetes. With established type 2 diabetes treated with fixed doses of insulin or insulin secretagogues, consistency in timing and carbohydrate content of meals is important. However, rapid-acting insulins and rapid-acting insulin secretagogues allow for more flexible food intake and lifestyle as in individuals with type 1 diabetes.
Increased physical activity by individuals with type 2 diabetes can lead to improved glycemia, decreased insulin resistance, and a reduction in cardiovascular risk factors, independent of change in body weight.
Resistance training is also effective in improving glycemia and, in the absence of proliferative retinopathy, people with type 2 diabetes can be encouraged to perform resistance exercise three times a week Adequate energy intake that provides appropriate weight gain is recommended during pregnancy. Weight loss is not recommended; however, for overweight and obese women with GDM, modest energy and carbohydrate restriction may be appropriate. MNT for GDM focuses on food choices for appropriate weight gain, normoglycemia, and absence of ketones.
Because GDM is a risk factor for subsequent type 2 diabetes, after delivery, lifestyle modifications aimed at reducing weight and increasing physical activity are recommended.
Prepregnancy MNT includes an individualized prenatal meal plan to optimize blood glucose control. Due to the continuous fetal draw of glucose from the mother, maintaining consistency of times and amounts of food eaten are important to avoidance of hypoglycemia. Plasma glucose monitoring and daily food records provide valuable information for insulin and meal plan adjustments. MNT for GDM primarily involves a carbohydrate-controlled meal plan that promotes optimal nutrition for maternal and fetal health with adequate energy for appropriate gestational weight gain, achievement and maintenance of normoglycemia, and absence of ketosis.
Specific nutrition and food recommendations are determined and subsequently modified based on individual assessment and self-monitoring of blood glucose. A recent large clinical trial reported that treatment of GDM with nutrition therapy, blood glucose monitoring, and insulin therapy as required for glycemic control reduced serious perinatal complications without increasing the rate of cesarean delivery as compared with routine care Maternal health—related quality of life was also improved.
Hypocaloric diets in obese women with GDM can result in ketonemia and ketonuria. Insufficient data are available to determine how such diets affect perinatal outcomes.
Daily food records, weekly weight checks, and ketone testing can be used to determine individual energy requirements and whether a woman is undereating to avoid insulin therapy.
Carbohydrate should be distributed throughout the day in three small- to moderate-sized meals and two to four snacks. An evening snack may be needed to prevent accelerated ketosis overnight. Carbohydrate is generally less well tolerated at breakfast than at other meals. Regular physical activity can help lower fasting and postprandial plasma glucose concentrations and may be used as an adjunct to improve maternal glycemia.
If insulin therapy is added to MNT, maintaining carbohydrate consistency at meals and snacks becomes a primary goal. Although most women with GDM revert to normal glucose tolerance postpartum, they are at increased risk of GDM in subsequent pregnancies and type 2 diabetes later in life. Lifestyle modifications after pregnancy aimed at reducing weight and increasing physical activity are recommended, as they reduce the risk of subsequent diabetes 26 , Breast-feeding is recommended for infants of women with preexisting diabetes or GDM; however, successful lactation requires planning and coordination of care In most situations, breast-feeding mothers require less insulin because of the calories expended with nursing.
Lactating women have reported fluctuations in blood glucose related to nursing sessions, often requiring a snack containing carbohydrate before or during breast-feeding Obese older adults with diabetes may benefit from modest energy restriction and an increase in physical activity; energy requirement may be less than for a younger individual of a similar weight. A daily multivitamin supplement may be appropriate, especially for those older adults with reduced energy intake.
Physical activity is needed to attenuate loss of lean body mass that can occur with energy restriction. Exercise training can significantly reduce the decline in maximal aerobic capacity that occurs with age, improve risk factors for atherosclerosis, slow the age-related decline in lean body mass, decrease central adiposity, and improve insulin sensitivity—all potentially beneficial for the older adult with diabetes 89 , However, exercise can also pose potential risks such as cardiac ischemia, musculoskeletal injuries, and hypoglycemia in patients treated with insulin or insulin secretagogues.
Reduction of protein intake to 0. MNT that favorably affects cardiovascular risk factors may also have a favorable effect on microvascular complications such as retinopathy and nephropathy.
Progression of diabetes complications may be modified by improving glycemic control, lowering blood pressure, and, potentially, reducing protein intake. In several studies of subjects with diabetes and microalbuminuria, urinary albumin excretion rate and decline in glomerular filtration were favorably influenced by reduction of protein intake to 0.
Although reduction of protein intake to 0. In individuals with diabetes and macroalbuminuria, reducing protein from all sources to 0. Although several studies have explored the potential benefit of plant proteins in place of animal proteins and specific animal proteins in diabetic individuals with microalbuninuria, the data are inconclusive 1 , Observational data suggest that dyslipidemia may increase albumin excretion and the rate of progression of diabetic nephropathy Elevation of plasma cholesterol in both type 1 and 2 diabetic subjects and plasma triglycerides in type 2 diabetic subjects were predictors of the need for renal replacement therapy Whereas these observations do not confirm that MNT will affect diabetic nephropathy, MNT designed to reduce the risk for CVD may have favorable effects on microvascular complications of diabetes.
For patients with diabetes at risk for CVD, diets high in fruits, vegetables, whole grains, and nuts may reduce the risk. In normotensive and hypertensive individuals, a reduced sodium intake e. In most individuals, a modest amount of weight loss beneficially affects blood pressure. In the EDIC Epidemiology of Diabetes Interventions and Complications study, the follow-up of the DCCT Diabetes Control and Complications Trial , intensive treatment of type 1 diabetic subjects during the DCCT study period improved glycemic control and significantly reduced the risk of the combined end point of cardiovascular death, myocardial infarction, and stroke Adjustment for A1C explained most of the treatment effect.
The risk reductions obtained with improved glycemia exceeded those that have been demonstrated for other interventions such as cholesterol and blood pressure reductions. There are no large-scale randomized trials to guide MNT recommendations for CVD risk reduction in individuals with type 2 diabetes. However, because CVD risk factors are similar in individuals with and without diabetes, benefits observed in nutrition studies in the general population are probably applicable to individuals with diabetes.
The previous section on dietary fat addresses the need to reduce intake of saturated and trans fatty acids and cholesterol. Hypertension, which is predictive of progression of micro- as well as macrovascular complications of diabetes, can be prevented and managed with interventions including weight loss, physical activity, moderation of alcohol intake, and diets such as DASH Dietary Approaches to Stop Hypertension.
The DASH diet emphasized fruits, vegetables, and low-fat dairy products; included whole grains, poultry, fish, and nuts; and was reduced in fats, red meat, sweets, and sugar-containing beverages 7 , , The effects of lifestyle interventions on hypertension appear to be additive.
Reduction in blood pressure in people with diabetes can occur with a modest amount of weight loss, although there is great variability in response 1 , 7. Regular aerobic physical activity, such as brisk walking, has an antihypertensive effect 7.
Although chronic excessive alcohol intake is associated with an increased risk of hypertension, light to moderate alcohol consumption is associated with reductions in blood pressure 7. Heart failure and peripheral vascular disease are common in individuals with diabetes, but little is known about the role of MNT in treating these complications. Alcohol intake is discouraged in patients at high risk for heart failure. Ingestion of 15—20 g glucose is the preferred treatment for hypoglycemia, although any form of carbohydrate that contains glucose may be used.
In individuals taking insulin or insulin secretagogues, changes in food intake, physical activity, and medication can contribute to the development of hypoglycemia.
The acute glycemic response correlates better with the glucose content than with the carbohydrate content of the food 1. Although pure glucose may be the preferred treatment, any form of carbohydrate that contains glucose will raise blood glucose Plant hormones are not nutrients , but chemicals that in small amounts promote and influence the growth,  development, and differentiation of cells and tissues.
The biosynthesis of plant hormones within plant tissues is often diffuse and not always localized. Plants lack glands to produce and store hormones, because, unlike animals—which have two circulatory systems lymphatic and cardiovascular powered by a heart that moves fluids around the body—plants use more passive means to move chemicals around their bodies.
Plants utilize simple chemicals as hormones, which move more easily through their tissues. They are often produced and used on a local basis within the plant body.
Plant cells produce hormones that affect even different regions of the cell producing the hormone. Hormones are transported within the plant by utilizing four types of movements. For localized movement, cytoplasmic streaming within cells and slow diffusion of ions and molecules between cells are utilized.
Vascular tissues are used to move hormones from one part of the plant to another; these include sieve tubes or phloem that move sugars from the leaves to the roots and flowers, and xylem that moves water and mineral solutes from the roots to the foliage.
Not all plant cells respond to hormones, but those cells that do are programmed to respond at specific points in their growth cycle. The greatest effects occur at specific stages during the cell's life, with diminished effects occurring before or after this period. Plants need hormones at very specific times during plant growth and at specific locations. They also need to disengage the effects that hormones have when they are no longer needed.
The production of hormones occurs very often at sites of active growth within the meristems , before cells have fully differentiated. After production, they are sometimes moved to other parts of the plant, where they cause an immediate effect; or they can be stored in cells to be released later. Plants use different pathways to regulate internal hormone quantities and moderate their effects; they can regulate the amount of chemicals used to biosynthesize hormones.
They can store them in cells, inactivate them, or cannibalise already-formed hormones by conjugating them with carbohydrates , amino acids , or peptides. Plants can also break down hormones chemically, effectively destroying them. Plant hormones frequently regulate the concentrations of other plant hormones. Because of these low concentrations, it has been very difficult to study plant hormones, and only since the late s have scientists been able to start piecing together their effects and relationships to plant physiology.
The earliest scientific observation and study dates to the s; the determination and observation of plant hormones and their identification was spread-out over the next 70 years.
Different hormones can be sorted into different classes, depending on their chemical structures. Within each class of hormone the exact structures vary, but they have similar physiological effects.
Initial research into plant hormones identified five major classes: Additionally there are also several other compounds that fulfill a similar function to the major hormones, but their status as bone fide hormones is still debated.
Abscisic acid also called ABA is one of the most important plant growth regulators. It was discovered and researched under two different names before its chemical properties were fully known, it was called dormin and abscicin II.
Once it was determined that the two compounds are the same, it was named abscisic acid. The name "abscisic acid" was given because it was found in high concentrations in newly abscissed or freshly fallen leaves. This class of PGR is composed of one chemical compound normally produced in the leaves of plants, originating from chloroplasts , especially when plants are under stress. In general, it acts as an inhibitory chemical compound that affects bud growth, and seed and bud dormancy. It mediates changes within the apical meristem, causing bud dormancy and the alteration of the last set of leaves into protective bud covers.
Since it was found in freshly abscissed leaves, it was thought to play a role in the processes of natural leaf drop, but further research has disproven this. In plant species from temperate parts of the world, it plays a role in leaf and seed dormancy by inhibiting growth, but, as it is dissipated from seeds or buds, growth begins.
In other plants, as ABA levels decrease, growth then commences as gibberellin levels increase. Without ABA, buds and seeds would start to grow during warm periods in winter and be killed when it froze again. Since ABA dissipates slowly from the tissues and its effects take time to be offset by other plant hormones, there is a delay in physiological pathways that provide some protection from premature growth.
It accumulates within seeds during fruit maturation, preventing seed germination within the fruit, or seed germination before winter. Abscisic acid's effects are degraded within plant tissues during cold temperatures or by its removal by water washing in out of the tissues, releasing the seeds and buds from dormancy.
In plants under water stress, ABA plays a role in closing the stomata. Soon after plants are water-stressed and the roots are deficient in water, a signal moves up to the leaves, causing the formation of ABA precursors there, which then move to the roots. The roots then release ABA, which is translocated to the foliage through the vascular system  and modulates the potassium and sodium uptake within the guard cells , which then lose turgidity , closing the stomata.
Just before the seed germinates, ABA levels decrease; during germination and early growth of the seedling, ABA levels decrease even more. As plants begin to produce shoots with fully functional leaves, ABA levels begin to increase, slowing down cellular growth in more "mature" areas of the plant.
Stress from water or predation affects ABA production and catabolism rates, mediating another cascade of effects that trigger specific responses from targeted cells. Scientists are still piecing together the complex interactions and effects of this and other phytohormones. Auxins are compounds that positively influence cell enlargement, bud formation and root initiation. They also promote the production of other hormones and in conjunction with cytokinins , they control the growth of stems, roots, and fruits, and convert stems into flowers.
They stimulate cambium , a subtype of meristem cells, to divide and in stems cause secondary xylem to differentiate. Auxins act to inhibit the growth of buds lower down the stems apical dominance , and also to promote lateral and adventitious root development and growth.
Leaf abscission is initiated by the growing point of a plant ceasing to produce auxins. Both the donors and the subjects brought in fresh stools, and the subjects were randomized to either get the donor stool, or get transplanted with their own collected feces. That was the placebo; you get your own back. High insulin sensitivity means low insulin resistance—the cause of both type 2 diabetes and prediabetes. The obese subjects started out around 20, and after an infusion of their own feces, they stayed around But, the group of obese donors getting the skinny similarly started out low, but shot up to near where the slim folks were.
The short-chain fatty acids produced by fiber-eating bacteria may contribute to the release of gut hormones that may be the cause of this beneficial improved insulin sensitivity.
But, within a few months, the bacterial composition returned back to baseline; so, the effects on the obese subjects were temporary. We can get similar benefits, though, by just feeding what few good gut bacteria we may already have. Feed them pork rinds, and they all die. Fecal transplants and probiotics are only temporary fixes, if we keep putting the wrong fuel into our gut.
However, such effects may abate once the high-fiber intake ceases. Newtown graffiti via flickr. Image has been modified. You may republish this material online or in print under our Creative Commons licence. You must attribute the article to NutritionFacts. If any changes are made to the original text or video, you must indicate, reasonably, what has changed about the article or video.
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