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Fiber
Fiber refers to a group of carbohydrate foods of plant origin (fruits, vegetables, grains, nuts and legumes) that the human gastrointestinal system cannot digest or absorb. Fiber has no caloric value and may be insoluble or soluble. Typical foods that are high in insoluble fiber are wheat bran, as found in bran flakes, bran muffins, or whole wheat bread. Insoluble fiber absorbs, but does not dissolve in, water, increasing gastrointestinal transit time. This fiber is not digested and contributes to stool bulk, occasionally acting as a laxative.
Foods high in soluble fiber include apples, citrus fruits, oat bran, oatmeal, dried beans and peas, and many vegetables. Soluble fiber slows gastric emptying, which can affect glycemic response if large enough quantities are eaten, and thus can be useful for people with diabetes. Soluble fibers are also known as "gel-forming" or "gummy" fibers because when dissolved in water, they form a gummy gel, which slows down glucose absorption and blunts postprandial glucose elevations. They likely accomplish this by disbursing the incoming food into various parts of this gel structure, retarding movement of nutrients toward the gut wall for absorption.
Digestive enzymes may also become caught in the gel, slowing their interaction with foodstuffs.
The current recommendation for fiber intake is to aim for a minimum of 20-35 grams of fiber per day. Research shows that people with type 2 diabetes can lower their blood glucose significantly by increasing the amount of fiber in their diet to approximately 50 grams per day. Joslin's Nutrition Guideline promotes this amount, as well, if the patient can tolerate it. Since the average fiber intake in the United States is approximately 8 grams per 1000 calories consumed, most people will find meeting the goal of 50 grams per day to be challenging and perhaps not realistic unless they take additional fiber supplements. When educating patients on increasing fiber intake, it is important that they be advised to increase fiber gradually (by 3–5 grams/day) to prevent bloating. Also, at least 8 cups of beverages need to be consumed each day, as a high-fiber diet without enough fluid can lead to constipation. People with gastroparesis may need a low fiber diet due to the slower emptying of stomach contents during digestion.
Soluble fibers have the advantage of being useful in treating dyslipidemia as compared to insoluble fibers. Oat bran (in oat bran cereal and oatmeal), pectin (in citrus fruits and apple peel), and legumes (dried beans and peas) all contain an ample amount of soluble fiber that help to lower the level of cholesterol in the blood.
Protein
Just as carbohydrates are constructed from building blocks of glucose, so are proteins made from amino acids constituents. Amino acids are also important components of hormones, antibodies, and bodily structural components. They provide energy to the body in the setting of carbohydrate insufficiency.
The recommended daily allowance (RDA) for protein is 0.8 g/kg of body weight. According to the Institute of Medicine, protein should constitute about 10% to 35% of the total calories for the day, although the ADA suggests that evidence doesn't support changing the usual protein intake of 15% to 20% of calories for people with diabetes and normal renal function. More healthful dietary protein sources include skinless poultry, fish and seafood, lean meat, legumes, and tofu.
With regard to type 2 diabetes, protein may aid in creating a sensation of fullness; maintaining muscle mass during weight reduction; and improving glucose uptake by muscles without increasing postprandial blood glucose. Thus, Joslin's Nutrition Guideline suggests aiming for approximately 20 to 30% of total calories from protein, as long as signs of diabetic kidney disease (microalbuminuria, increased serum creatinine or decreased creatinine clearance) are absent.
Fat
Fat (primarily triglycerides) is a dense energy source, providing 9 calories/gram in comparison to carbohydrate or protein, which provide 4 calories/gram.) However, because fat is metabolized via different pathways than carbohydrate and protein, it has less immediate effect on blood glucose levels. Yet, fat delays the emptying of food into the intestines, and thus may slow down the rise in the blood glucose if included as part of a mixed meal. A high-fat meal may result in a high blood glucose many hours later than expected due to delayed gastric emptying of carbohydrate and protein.
Fat is also a component of certain molecules and structures in the body, though not all of these fats are manufactured by the body. Some of these essential fats (linoleic and linolenic acids) must therefore be included as part of a normal diet.
People with diabetes often have elevated plasma cholesterol and triglyceride levels and lower levels of high-density lipoproteins (HDL) than nondiabetic individuals. Evidence suggests that lowering plasma lipid levels can reduce the occurrence of cardiovascular disease either through dietary adjustments or, if needed, with medications.
Dietary fat is digested into fatty acids, which are then absorbed into the bloodstream or stored. When the level of insulin is low, such as during weight loss or ketoacidosis, the opposite occurs -- fat comes out of storage and is an alternative source of energy. The by-products of the use of fat as an energy source are known as ketones. If ketones are seen during weight loss in a person with type 2 diabetes, despite well-controlled blood glucose levels, they indicate that the meal plan is successful. However, the presence of ketones in a person with type 1 diabetes with high blood glucose levels due to sickness or missed insulin injections shows a dangerous insulin insufficiency and indicates that more insulin is needed immediately.
Cholesterol and triglycerides travel in the bloodstream as part of lipoprotein particles. Lipoproteins are classified by density and size. Low density lipoproteins (LDL), or "bad cholesterol," usually carry cholesterol. High levels of LDL are dangerous because they deposit the cholesterol in the vascular epithelium. However, high-density lipoproteins (HDL), the so-called "good cholesterol," carry cholesterol away from blood vessel walls, back to the liver, where it is disposed of.
Triglycerides are made up of three fatty acid molecules. Fatty acids can be saturated or unsaturated. The choice of fats is important. In general, most saturated fats can increase cholesterol levels and are more harmful than unsaturated fats. Stearic acid and the medium-chain triglycerides are exceptions to this rule. Animal fats, which are usually solid at room temperature, are saturated fats. Palm and coconut oil are also saturated. Saturated fats raise blood cholesterol levels by interfering with the entry of cholesterol into cells. This causes cholesterol to remain in the blood stream longer and to become part of the plaque that builds up in the blood vessels.
Cholesterol intake should be limited to less than 200 mg/day for people with diabetes. By comparison, the average American consumes between 200 and 300 mg of cholesterol per day.
Trans fat is a type of fat formed from partial hydrogenation of oil, a chemical process that changes a liquid oil into a solid fat. The process involves adding hydrogen to liquid oil and turning it into solid or semisolid fat. Transfats are found in many processed foods, including snack foods, cookies, some margarines and fast foods. Transfats raise LDL-cholesterol level and significantly increase the risk for coronary artery disease more than any type of fat. For this reason, it should be limited as much as possible. As of January 1, 2006, the FDA has required that all food manufacturers list transfat on the nutrition label, along with saturated fat and dietary cholesterol. Joslin's Nutrition Guideline recommends complete elimination of trans fat from the diabetes meal plan.
Monounsaturated fats such as olive, peanut, and canola oils, and polyunsaturated fats, such as corn, soy, safflower and sunflower oils, may help reduce cholesterol levels and are therefore preferred over saturated fats and trans fats. Unsaturated fats are liquid at room temperature, whereas saturated fats and trans fats are solid. However, unsaturated fats contain just as many calories as all other fats. Remember, too, that if these "good" oils are hydrogenated (as may be indicated on the ingredient label) they can raise the LDL (the "bad" cholesterol).
Fish is a source of two types of omega-3 fatty acids: eicosapentanoic acid (EPA) and docosahexanoic acid (DHA). Omega-3 fatty acids may help lower the risk of cardiovascular disease by in reducing triglyceride and blood pressure levels, and decreasing the risk of arrhythmias. These fatty acids may offer other health benefits beyond heart health, as well.
Good sources of omega-3 fatty acids include fatty fish, such as salmon, herring, mackerel, trout and sardines. The American Heart Association recommends eating at least two servings of non-fried, fatty fish per week. Supplements may be recommended for people who are not able to consume adequate omega-3 fatty acids by food alone. The use of such supplements should be discussed with and monitored by a healthcare provider, and this is especially important for people who are taking blood-thinning medications.
Another type of omega-3 fatty acid, called alpha-linolenic acid, found in walnuts, canola oil, flaxseed and olive oil, is also an essential fatty acid and is thought to help decrease blood clotting and decrease inflammatory processes in the body. Patients should be encouraged to obtain alphalinolenic acid from food sources rather than from supplements.
The current ADA recommendation is to base the percentage of calories that may be derived from fat on the patient's specific nutritional assessment, treatment goals, and lipid levels. A general guideline, based on the USDA Dietary Guidelines for Americans 2005, for those who are at a healthy weight and whose lipid levels are not a concern would be to limit fat intake to 20% to 35% of total calories; of this, less than 10% should be saturated (although the ADA does recommend that less than 7% of calories come from saturated fat).
Joslin's Nutrition Guideline for overweight or obese patients with type 2 diabetes recommends aiming for 30 to 35% of calories from fat, and limiting saturated fat to less than 10% of total calories or to less than 7% of total calories if LDL cholesterol is greater than 100 mg/dl. Polyunsaturated fat should comprise no more than 10% of calories, and the remaining 15 to 20% of total calories should come from monounsaturated fats
Two dietary substances that have recently attracted attention, called plant stanols and plant sterols, have the ability to lower blood cholesterol levels, and their daily consumption is recommended as part of a "heart healthy" diet. It has been known for more than 50 years that these substances can lower blood cholesterol levels. Plant stanols and sterols are found naturally in many fruits, vegetables, nuts, seeds, legumes and vegetable oils, although the amounts in these foods are not high enough to significantly impact cholesterol levels. Some food manufacturers have developed products that contain appreciable amounts of either of these ingredients. Plant stanols and sterols have been added to certain margarines, juices and yogurt. These substances block dietary cholesterol absorption, resulting in a significant lowering of total serum and LDL cholesterol levels averaging 10%. The National Cholesterol Education Program's ATP III Guidelines recommend 2 grams plant stanols as part of a daily diet that is low in saturated fat and cholesterol to help reduce heart disease.
Next Joslin Excerpt: All about sweeteners
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Please Note: Reasonable measures have been taken to ensure the accuracy of the information presented herein. However, drug information may change at any time and without notice and all readers are cautioned to consult the manufacturer's packaging inserts before prescribing medication. Joslin Diabetes Center cannot ensure the safety or efficacy of any product described in this book.
Professionals must use their own professional medical judgment, training and experience and should not rely solely on the information provided in this book to make recommendations to patients with regard to nutrition or exercise or to prescribe medications.
This book is not intended to encourage the treatment of illness, disease or any other medical problem by the layperson. Any application of the recommendations set forth in the following pages is at the reader's discretion and sole risk. Laypersons are strongly advised to consult a physician or other healthcare professional before altering or undertaking any exercise or nutritional program or before taking any medication referred to in this book.
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