Study finds those eating low-fat diets with high insulin levels are most prone to weight gain

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It’s difficult to avoid the doom-laden statistics concerning rates of overweight and obesity. And at the same time we’ll no doubt be aware of the standard advice for those wanting to lose weight: ‘eat less and exercise more.’ The problem is, the evidence suggests that neither of these approaches is particularly effective for the purposes of weight loss in the long term.

Some researchers and scientists are in the process of thinking a little more creatively about the ‘obesity epidemic’. What, some are asking, if weight is not determined simply by the relative amounts of calories taken in and those that are metabolised by the body?

One important factor here concerns appetite. It makes sense for individuals who want to curb any tendency to overeat to consume foods that tend to be appetite-sating relative to other foods. The usual advice is geared toward getting individuals to eat a fibre-rich diet because, supposedly, ‘fibre fills us up’ and helps us ‘feel full for longer’. Actually, there is good evidence that, overall, protein is the part of the diet that packs really appetite-sating power.

Another factor well worth considering concerns the tendency for food to predispose to fatty accumulation in the body. While it seems obvious that the major dietary spectre in this respect is fat, the reality is that the prime fat-producing hormone in the body is insulin. And insulin, as we know, is secreted chiefly in response to intake or carbohydrate.

Some have theorised that weight gain can be driven by a glut of insulin. Perhaps the most famous/infamous person to put forward this theory was the late Dr Robert Atkins. Others have come in his wake. Recently, new life has been breathed into this concept by Gary Taubes, author of ‘Good Calories Bad Calories: Challenging the conventional wisdom on diet, weight control, and disease’. I’ve not read this book, but know enough about it and Taubes’ previous work to recommend it to anyone who takes a keen interest in their (or other people’s) health.

While weight gain is unlikely to be solely about insulin, my belief is that it is likely a major factor here. Some support for this has come from a study published this month in the American Journal of Clinical Nutrition [1]. The researchers in this study basically assessed insulin levels (actually insulin levels 30 minutes after giving individuals 75 g of glucose) in 276 people and then followed them for an average of 6 years each. This insulin measurement can be taken as a proxy measure of an individual’s ability to handle carbohydrate (sugar) in the system.

The authors looked at the relationship between insulin levels and certain measurements including weight gain and waist circumference. They also, analysed whether there was any difference in results in those eating a low-fat diet compared to those eating a higher fat diet.

Here, essentially, is what they found:

In individuals eating a lower fat diet, higher levels of insulin were associated with an increased risk of weight gain and increase in waist circumference.

This association was not evident in individuals eating a higher-fat diet.

Overall, in the low-fat eating group, individuals with the highest insulin levels gained 4.5 kg (9.9 pounds) more than those with low insulin levels.

So, what are we to make of all of this? The most obvious thing to come out of this study is that higher insulin levels are associated with increased tendency to gain weight. This finding clearly lends support to the idea that insulin may have a key role to play in weight gain.

But why would this association be only evident in those eating a lower-fat diet? I don’t know for sure, but it’s likely to do less with fat, and more to do with carbohydrate: Because high insulin levels are generally a sign that individuals are not coping well with carbohydrate in the body, one might imagine that eating a carb-rich diet is more likely to land these people in trouble than those eating a lower carb diet. Those eating a low-fat diet tend to eat a diet rich in carb, and this may explain why these individuals were the ones most prone to weight gain.

Of course the corollary here is that individuals eating a higher-fat, and therefore lower carb, diet are likely to be less prone to weight gain induced by insulin, right? This finding doesn’t prove anything. But it does sure seem to lend some support to the concept of carbohydrate-control for weight loss.


1. Chaput JP, et al. A novel interaction between dietary composition and insulin secretion: effects on weight gain in the Quebec Family Study. Am J Clin Nutr 2008;87:303-309

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