Eat as Much as You Like and Lose Weight?

Summarized by Robert W. Griffith, MD
June 30, 2005

Introduction

One of the problems with dieting is that it usually means eating less! So any proposal for a change in eating habits that still allows ad libitum consumption is more likely to succeed than restrictive approaches. An alternative to the popular low-carbohydrate diet and the low-fat diet has been researched by scientists from Boston, Massachusetts. This is the low-glycemic load diet, which allows unrestricted intake of carbohydrate from low glycemic-index foods. A low glycemic index diet contains non-starch vegetables, fruit, legumes, whole grains, nuts, and dairy produce. The study was done to examine the effectiveness of ad libitum low glycemic index diet as an alternative to a conventional low-fat diet on cardiovascular risk factors, including body weight.

What was done

Thirty-four volunteers aged between 18 and 35, with a body mass index (BMI) over 27 but body weight below 300 lbs (or 136 kg), were enrolled. There were 30 women and 4 men.

They were randomly allocated to take a low glycemic index diet or a low-fat diet, with 6 months of monthly 1-hour dietary counseling sessions, and then 6 months of less intense follow-up (just 2 counseling sessions in all).

The recommended low glycemic index diet comprised non-starchy vegetables, fruit, peas, beans, nuts, and dairy products. The participants in this group "were to eat carbohydrate with protein and healthful fat at every meal and snack, and to eat to satiety and snack when hungry". A low glycemic index diet pyramid was provided, yielding, if followed, 45-50% of energy from carbohydrate, 30-35% of energy from fat, and the remainder from protein.

The conventional low-fat diet was based on the American Diabetes Association's diabetes food pyramid, yielding 55-60% of energy from carbohydrate, less than 30% energy from fat, and the remainder from protein.

All participants received the same counseling about physical activity and behavioral therapy (help with self-control). The volunteers kept 7-day food diaries at baseline, 3, 6, and 12 months, to ensure that they were following their allocated recommendations.

Weight, height, blood pressure, blood lipids, blood glucose, serum insulin, and plasminogen activator inhibitor (PAI-1)¹ were measured at baseline, 6 and 12 months.

What was found

Of the 34 original enrollees, 11 dropped out during the year - there was one pregnancy, two illnesses, and 8 who discontinued without explanation. Eleven people following the low glycemic index diet and 12 following the low-fat diet completed the 1-year study.

Body weight decreased significantly in both the groups; by 6 months, the low glycemic index diet group had lost 8.4% of their starting weight, and the low-fat diet group had lost 7.8%. After one year, these values were -7.8% and -6.1%, respectively.

Blood triglyceride levels decreased by 37% in the low glycemic index group compared with 19% in the low-fat group. And PAI-1 levels decreased by 39% in the low glycemic index group, but increased by 33% in the low-fat group. Insulin sensitivity increased significantly in both groups.

There were no significant changes in blood pressure, the other blood lipids, and blood glucose levels.

What these results mean

While both approaches to dieting had similar beneficial effects on body weight, the low glycemic index diet had a more favorable effect on triglyceride and PAI-1 levels. Both of these blood substances are directly linked with increased risk of a cardiovascular event (e.g. heart attack, stroke, or severe angina).

Almost more important than this, however, is the ad libitum nature of the low glycemic index diet. A low-fat diet is restrictive, and difficult to follow after some time. There's no doubt that a diet where you are told you can eat as much as you like is likely to find favor in the long term, and will certainly prove more effective in the long run.

Source

• Effects of an ad libitum low-glycemic load diet on cardiovascular disease risk factors in obese young adults. CB. Ebbeling, MM. Leidig, KB. Sinclair,  et al., Am J Clin Nutr, 2005, vol. 81, pp. 976--982

Footnotes
1. PAI-1 is produced by the endothelium and liver and is also present in platelets. The synthesis of PAI-1 is increased by high glucose or insulin levels. PAI-1 levels are elevated in insulin resistance, which is associated with an increased risk of coronary artery disease.

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