Less Fat and More Fiber is Key

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Many promoters of fad-diets, including Atkins, Sears (Zone Diet), and Agatston (South Beach Diet) have claimed high-carbohydrate diets promote obesity. The rationale given is that such diets, particularly if they have a high glycemic index (GI), cause an over stimulation of insulin production, which stimulates appetite, leading to excessive hunger and overeating, and the carbohydrates being converted to fat.

Even some well-respected researchers have published studies suggesting high carbohydrate diets, composed largely of high-GI foods, lead to increased ad libitum calorie intake. However, the problems with these studies was that they all failed to control for other factors known to impact appetite and ad libitum calorie intake, such as fiber, protein, and energy density (ED).

Nevertheless, the unsubstantiated belief that a high-carbohydrate diet, composed largely of high GI foods and having a high glycemic load (GL), enhances appetite and promotes overeating, persists among the general public and some researchers and health professionals.

Do High GI/GL Diets Promote Over Eating?

A recent study examined the impact of feeding 39 people diets with the same ED and consisting of either high or low GI foods and similar amounts of fat, protein, carbohydrate and fiber for 8 days. Subjects were allowed to eat as much as they wanted.

Blood sugar and insulin levels were measured throughout the day on both diets on the first and eighth day. The results showed no significant differences for hunger, fullness, or desire-to-eat ratings on the high- and low-GI diets.

There was also no correlation between appetite ratings and either the blood glucose or insulin responses. The subjects choose to consume the same amount of calories on both the high- and low-GI diets.1

The results of this study clearly undermine claims made by fad diet book authors and some researchers linking a diet with a lot of high-GI foods and a high GL with an increased appetite, overeating and obesity.

Less Fat and More Fiber is Key

A study of U.S. adults age 20-59 years old examined the relationship between diet and BMI.

In men, the result showed an increased percent of dietary fat was most strongly associated with a greater BMI. While higher fiber was correlated with a lower BMI, the association did not reach statistical significance.

By contrast, the women in this study that consumed more fiber were much less likely to be overweight or obese, but the correlation with percent of fat intake and body weight was much weaker than in men and not statistically significant. The relative risk of being overweight or obese for women in this study is shown in the figure below.2

As the figure below shows, the women who consumed a diet high in fat, as well as fiber, were more than three and a half times as likely to be overweight or obese as those who consumed a diet high in fiber and low in fat. However, the women who consumed a low-fat diet that was also low in fiber were about five times as likely to be overweight or obese as those who consumed a low-fat and high-fiber diet.

Less Fat and More Fiber Less Fat and More Fiber is Key


The data from this study, combined with other studies, strongly suggests that both men and women would be far less likely to become overweight or obese if they consumed diets with a lot more fiber and a lot less fat than is the norm today.

It should be noted that only about 5% of Americans consume what the newest U.S. Dietary Guidelines called an adequate intake for fiber (14 g per 1,000 calories).

Bottom Line: A diet composed largely of fruits, vegetables and whole grains that is low in fat and fat-rich foods promotes weight loss without hunger. This is largely because such a diet has a lower calorie density, less fat, and more fiber, each of which increases satiety per calorie and so reduces ad libitum calorie intake. Such a diet can easily achieve the adequate intake for fiber and meet all other nutrient needs for young and middle-aged adults.

By James J. Kenney, PhD, RD, FACN.

References: 1. Diabetes Care 2005;28:2123-9

2. J Am Diet Assoc. 2005;105:1365-72

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