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Insulin Levels Can Predict Weight Loss on Certain Diets

Posted: Friday, May 25, 2007

Individual differences in insulin secretion may explain why some individuals respond well to either a low-fat diet or low-glycemic-load diet, whereas others do not, a randomized study suggests.
The findings imply that a simple, baseline oral glucose tolerance test to assess serum insulin concentration may help clinicians and dieticians choose weight-loss strategies for obese subjects.

Dr. Ebbeling stated that, "We often ask, why do people succeed with a conventional low-fat diet while others who are following the exact same diet can't keep weight off?" "Usually we answer this question with something like: 'the ones who succeed are more motivated, or have more willpower, or they're more able to stick with a diet while others are not as motivated.' But this really is not a complete answer to the question. So we sought to determine if biology had something to do with it."

Ebbeling and colleagues randomized 73 obese young adults (aged 18 - 35 years) to a 6-month dietary intervention: either a low–glycemic-load diet (40% carbohydrate, 35% fat, and rich in low–glycemic index foods), or a low-fat diet (55% carbohydrate and 20% fat). At baseline, all subjects were given an oral glucose tolerance test to check for insulin concentration after 75 g of dextrose. Subjects adhered "intensively" to diets for 6 months, then were followed up for an additional 12 months.

For the group as a whole, changes in body weight and body fat percentage at 18 months did not differ between the 2 diet groups; however, when stratified according to baseline glucose tolerance test, subjects with above-median insulin concentration (> 57.5 µlU/mL) lost significantly more weight on the low–glycemic-load diet than they did on the low-fat diet by 18 months. In contrast, subjects with insulin concentrations below median levels (≤ 57.5 µlU/mL) during the baseline glucose tolerance test had similar outcomes, regardless of to which diet they had been randomized.

Differences between the diets were seen in effects of the different diets on lipid parameters, regardless of baseline glucose tolerance tests. The low–glycemic-load diet produced significant improvements in high-density lipoprotein (HDL) cholesterol and triglyceride profiles, whereas the low-fat diet produced significantly greater reductions in low-density lipoprotein (LDL) cholesterol levels.

"Regardless of insulin secretion at baseline, the LGL [low–glycemic-load] diet has beneficial effects on HDL cholesterol and triglycerides that were not seen on the LF [low-fat] diet, while LDL cholesterol decreased in the participants in the LF diet, but not the LGL diet," Dr. Ebbeling said. "This is just is speculation on our part, but an LGL diet that also substitutes unsaturated fats for fats may be even more beneficial for everyone, since the beneficial effects on insulin, cholesterol, and triglycerides with the LGL diet were seen regardless of insulin secretion."

“Spikes in insulin concentration after a meal are believed to promote feelings of hunger and can lead to overeating,” and "people who are 'high insulin secreters' may be particularly susceptible to weight gain with conventional low fat diets that are higher in carbohydrates, " says Dr. Ebbeling. By contrast, low insulin secreters seem to do the same on either the low-fat diet or the low–glycemic-load diet, she continued. "It seems that people who are high insulin secreters may be particularly susceptible to weight gain and may be more challenged to lose weight with a conventional low fat diet."

Dr. Ebbeling states that, "From a clinical perspective, our findings provide rationale for individualizing weight loss diets or diet prescription based on an oral glucose tolerance test."

Source: Diabetes In Control: JAMA. 2007;297:2092-2102