Fiber and Obesity

Diabesity: is the term coined to describe the common concurrence of diabetes and obesity. In the United States, Type II diabetes accounts for more than 97% of the diabetes seen and between 60-80% of Type II diabetic individuals are obese; thus, approximately 9-9 million Americans suffer from "diabesity". Increased intake of dietary fiber offers many advantages to obese diabetic individuals. In previous reports [1, 2, 3], we outlined these benefits which will be summarized here. Our experience with the use of high fiber, weight-reducing diets for management of obese diabetic and non-diabetic individuals will be summarized.

Both soluble and insoluble fiber may contribute to weight control. Soluble fiber slows gastric emptying, decreases mixing of foods and digestive enzymes in the small intestine, and is readily fermented to short-chain fatty acids in the colon. Insoluble fiber accelerates passage of food into the colon, decreases digestion time of foods, physically prevents interaction between digestive enzymes and nutrients, and produces a fullness throughout the gastrointestinal tract.

High fiber diets are very effective in the management of lean Type II diabetic individuals. They lower blood glucose values, diminish need for insulin or oral hypoglycemic agents, increase insulin sensitivity, decrease blood pressure, and drop serum cholesterol and triglycerides. Since modest amounts of weight loss offer major benefits for diabetic individuals, the incorporation of generous amounts of dietary fiber into energy restricted diets acts synergistically to improve the diabetic condition and enhance weight loss.

After learning about the effectiveness of HCF diets for management of lean Type II diabetic individuals we developed high fiber weight reducing diets for obese Type II diabetic individuals. This experience will be briefly reviewed. While most of our research experience has been with high fiber diets for obese diabetic individuals, we have applied this experience to the management of obese non-diabetic individuals in our clinical practice.

THE LEXINGTON EXPERIENCE

a. Short-term experience

Satiety was examined in a pilot experiment to determine the acceptability of 800 kcal (about 3 kcal/pound) diets. We used a random allocation, crossover design to compare high fiber and low fiber 800 kcal diets. Four obese diabetic men weighing approximately 250 pounds were fed high fiber diets providing 32 grams dietary fiber per 800 kcal for 10 days and low fiber diets providing 8 grams of dietary fiber per 800 kcal for 10 days. Two men received the low fiber diet first and two men received the high fiber diet first. Six times daily, before and after breakfast, lunch and dinner, subjects indicated their feeling of hunger or satiety by circling the descriptive words and putting a mark on a line to indicate their feeling of hunger or satiety.

On the high fiber diet, the feeling of satiety was higher at every time point than on the low fiber diet. Even though only four subjects participated in this experiment, these differences were statistically significant at every time point except before breakfast.

Diets were specifically designed to be high in dietary fiber and well balanced in nutrition. To examine the effects of careful adherence to these diets we treated 22 men on the metabolic ward. They received high fiber diets, with these levels of energy restriction:

•	Mild energy restriction- These high fiber diets provided approximately 9 kcal/pound (2000 kcal/day for a person weighing 250 pounds) and 60 grams of fiber/day;
•	Moderate energy restriction- These high fiber diets provided approximately 5 kcal/pound (1250 kcal/day for a person weighing 250 pounds) and 45 grams of fiber/day;
•	Severe energy restriction- These high fiber diets provided approximately 3 kcal/pound (750 kcal/day for a person weighing 250 pounds) and 30 grams of dietary fiber/day.

Weight loss
Since these diets were lower in sodium than their usual diets and for other reasons, some of the weight loss was related to loss of water. While on these weight-reducing diets on the metabolic research ward these subjects were encouraged to be active; some walked several miles per day but most were fairly sedentary. On approximately 2000 kcal/day (8 kcal/pound), seven men lost an average of 1.8 pounds per week over a three-week period. On approximately 1250 kcal/day (5 kcal/pound), seven men lost 3.6 pounds per week. On 800 kcal/day (3 kcal/pound), seven men lost 6.4 pounds per week or 19 pounds during their three-week stay on the metabolic research ward. Most men found the diets acceptable and continued on high fiber, weight reducing diets when discharged from the metabolic ward.

Insulin doses decreased dramatically on all weight-reducing diets. Usually insulin doses were decreased about 50% when starting these weight-reducing diets and were decreased further to avoid hypoglycemia. Figure 5.2 shows the response of an individual to an 800 kcal diet. Mild energy restriction (8 kcal/pound) decreased insulin requirements by 59% allowing insulin to be discontinued in 6 or 7 subjects (86%). Moderate energy restriction (5 kcal/pound) decreased insulin requirements by 85% allowing insulin to be discontinued in 86% of subjects. Severe energy restriction (3 kcal/pound) decreased insulin requirements by 98% allowing insulin to be discontinued in 7 of 8 subjects (88%). Figure 5.3 illustrates the time course of reduction in insulin dose for diabetic men treated with severe energy restricted diets.

Plasma glucose responses occurred rapidly and mandated a rapid reduction in insulin doses. We attempted to maintain plasma glucose values of 150-200 mg/dl until insulin was discontinued. Final glucose values, after insulin was discontinued in 87% of subjects, were about 155 mg/dl, 33% lower than initial values.

Serum lipid values plummeted in all subjects. Average serum cholesterol values decreased 23% and triglycerides decreased 55%.

Blood pressure values, measured three times daily, also decreased significantly with reduction of more than 10% for both systolic and diastolic values

b. Long-term studies

While these obese diabetic individuals responded well to high fiber, weight-reducing diets in the hospital, the critical question is their long-term weight maintenance. We were not able to provide an intensive weight-maintenance education program for these individuals but did see them at three to six month intervals and encouraged adherence to the high fiber diet and to a walking program.

For home management the dietitians instructed most individuals on use of a moderate-energy restricted diet to provide about 5 kcal/pound or 1000-1500 kcal per day. These diets provided about 35-40 grams of fiber/1000 kcal. We obtained follow-up information on 25 obese, diabetic subjects who had participated in a protocol similar to that outlined above. All had been receiving insulin therapy for their diabetes and entered the metabolic ward for a weight-reducing program of approximately 3 weeks duration. We obtained follow-up information after an average of 2.5 years.

Weight responses. Subjects lost an average of 27 pounds (11.5% of initial body weight). After 2.5 years they were maintaining a weight loss of 15 pounds which represents 6.5% of initial body weight. Expressed differently, they were maintaining 56% of their weight loss at 2.5 years.

Insulin doses fell dramatically with initial weight loss with average values dropping 96%. Insulin was discontinued in 22 of 25 subjects (88%) with their weight loss. However, during the 2.5 year interval, insulin was restarted in nine subjects; thus, 12 of 25 (48%) were taking insulin at the time of follow-up.

Fasting plasma glucose values plummeted despite the major reduction in insulin dose. The values at the nadir of body weight were 43% lower than initial values. With weight gain, glucose values increased and, despite an increase in insulin dose, were 86% of initial values at 2.5 years of follow-up. Glycemic control, as summarized in Table 5.4, was greatly improved on the weight loss program and was better, on average, at 2.5 years of follow-up than initial values.

THE WORLDWIDE EXPERIENCE

Satiety. Blundell and Burley [4, 5] have reviewed the effects of fiber intake on satiety. They summarized three types of studies: studies using fiber supplements; studies using fiber-supplemented foods; and studies using high fiber foods. With fiber supplements such as guar gum or fiber tables in seven of 11 studies investigators reported either decreased hunger or reduced food intake [6,7,8,9,10,11,12e,13,14,15,16]. With fiber-supplemented foods in eight of 11 studies investigators reported either decreased hunger or reduced food intake [17,18,19,20,21,22,23,24,25,26,27]. With high-fiber foods in four of four studies investigators reported either decreased hunger or reduced food intake [28,29,30,31]. Subsequent studies [32] have confirmed and extended prior investigations. These observations led to the conclusion that dietary fiber intake decreases energy intake and contributes to fullness or satiation and maintains between meal feeling of satiety [3].

Weight loss. High-fiber, low-energy dense foods are widely used in weight-reducing programs for non-diabetic or diabetic patients [33,34,35,36]. The typical diet recommended for moderate weight loss is generous in complex carbohydrate and fiber and limited in fat and simple sugars [37]. While these high-fiber diets are widely used, there are no persuasive clinical studies documenting that diets providing generous amounts of fiber-rich foods are more effective in promoting weight-loss that equi-caloric diets restricted in high-fiber foods. These clinical studies are difficult to perform because subjects cannot be blinded to their dietary assignment. Clinical studies in this area are required to clearly demonstrate that high-fiber, high-carbohydrate, low-fat diets are superior to equi-caloric low-fiber, high-carbohydrate, low-fat diets.

While high-fiber food rich diets have not been documented to promote greater weight loss than control diets, the use of fiber supplements is accompanied by significantly greater weight loss than placebo [12,14,38,39].

Weight maintenance. The benefits of high fiber intakes for weight maintenance are not established scientifically. In our clinical practice we encourage intake of at least five servings of vegetables or fruits daily. While our clinical experience tells us that this high fiber intake contributes to successful weight maintenance, we do not have scientific dat to support this impression. The studies of Weinser and colleagues [33] also suggest that intake of high fiber foods contributes to successful weight maintenance.

CONCLUSIONS

The benefits of high-fiber, weight-reducing diets for diabetic individuals are clear cut. These diets enable diabetic individuals to lose weight and maintain weight loss long-term. These diets also decrease blood glucose values, diminish need for oral hypoglycemic agents or insulin, lower blood pressure, and drop serum lipid values. Fiber supplements are documented to enhance weight loss with a hypocaloric diet. High fiber diets act mechanically, physiologically and chemically to decrease hunger and enhance between meal satiety.