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June 12, 2014

High carbohydrate diets

by Helene van den Berg

On a high-carbohydrate diet, glucose is used by the cells for energy and about 2/3 of body cells require insulin in order to use glucose. Excessive amounts of blood glucose are the primary cause of the complications of diabetes and obesity, when glucose reacts with body proteins (glycosolated proteins) and change their behavior. After a high-carbohydrate meal, the blood glucose will rise for an hour or two after a meal, the beta cells in the pancreas release insulin to cause uptake of glucose in the cells. In liver and muscle cells, more glucose is taken in than is needed and stored as glycogen (300-500g carbohydrates are stored). Many sugar-containing foods produce a high glycemic response, promoting postprandial carbohydrate oxidation at the expense of fat oxidation, leading to body fat gain.

Increased levels of glucose and insulin will inhibit lipolysis,(breaking down of fats), reduce the amounts of free fatty acids (FFA’s) and consequently reduce fat oxidation. Obese persons inability to mobilize and oxidize fat, are linked to long-term hyperinsulinemia. Postprandial increases in glucose will indeed reduce blood FFA’s and fat oxidation short term, but the question remains (in relation to body weight control), whether these effects persist for longer than 24 hours. In a study done on moderately obese men, the differences in fat and carbohydrate oxidation during the day, were completely compensated for during the night. Therefore more trials are needed to confirm that high-GI diets (high in sucrose) will shift metabolism to fat storage.

A study has shown that the body weight of formerly obese women decreased significantly with a starch diet, but no changes were observed during the fat and sucrose diets, due to the following reasons: increased satiety (fullness), due to the high fiber content and volume, and less palatability, than the sucrose and fat diets. The higher energy intake with the sucrose diet was explained by the large amount of sucrose-containing drinks in this diet. Fluids are less efficient in increasing satiety and suppressing food intake than are solid foods. The weight gaining effect of carbohydrate drinks have been confirmed in numerous studies – especially in children overindulging in sugar-sweetened drinks. The combination of the frequent use of carbohydrate-sweetened beverages (high-fructose corn syrup) and an inactive lifestyle, which reduces the metabolic demand for fat as fuel, considerably increase the risk of weight gain!!.

Critics argue that low carbohydrate diets require minimizing vegetable and fruit consumption, which robs the body of important vitamins and minerals and imply that vegetables and fruit are loaded with carbohydrates. Contrary to these arguments, the sugar in fruit is fructose and has very little effect on insulin levels in obese subjects; and fruit sugars mostly contain water and is not calorie-dense; and sweet fruits and berries in their natural form are high in fiber, which assist the absorption of sugar in the gut.

Most vegetables are low/moderate-carbohydrate foods (e.g. broccoli, spinach, cauliflower, peppers etc.), although potatoes, carrots, rice and corn, have high concentrations of starch. Some individuals choose to avoid vegetables to minimize carbohydrate intake, but raw fruits and vegetables are packed with vitamins, flavonoids and sugar alcohols, with some of them guarding the over-absorption of sugars in the human digestive system. Low-carbohydrate diets recommend multi-vitamin and mineral supplements, not because they are nutritionally deficient, but the body goes through a “shock” if the diet is changed quickly. During this period of adjustment it needs extra vitamins and minerals, because the body releases excess fluids that were stored during high-carbohydrate eating.

Is it true?. The body does not need to work as hard to get it’s energy with high-carbohydrate diets, because most carbohydrates break down readily into glucose in the bloodstream?. Not really!. Dietary carbohydrates are broken down into glucose, but does not remain in the bloodstream for long. It’s presence stimulates the beta cells in the pancreas to release insulin, causing the body cells to take in glucose, and fat cells to take in fatty acids and store them. As the blood glucose level falls, the amount of insulin released is reduced – within an hour or two after eating. High refined carbohydrate diets require more insulin production and release, than low-carbohydrate diets and increases the incidence of metabolic disorders (diabetes). Also, the nature of the carbohydrates ingested, has to be considered. Some are indigestible in humans (cellulose), some are poorly digested (amylase starch variant) and some require considerable processing to be converted to absorbable forms. Uncooked and unprocessed foods are much harder to absorb and do not raise the glucose levels as much as cooking and mechanical processing.

 

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