In a paper presented at the World Congress on Insulin Resistance Dr. Mona Boaz and her colleagues at the Wolfson Medical Center in Holon, Israel, presented a meta-analysis of four recent studies on the effectiveness of low-carbohydrate and low-fat diets in reducing and maintaining weight loss.


What is meta-analysis?

A meta-analysis combines the results of several studies that address a set of related research hypotheses. For instance, if the research hypothesis is that calorie reduction should result in weight loss, then it should be possible to combine several studies that test this hypothesis.  What’s the advantage?

When we deal with subjects that don’t lend themselves to the gold standard of randomized, double-blind, placebo-controlled studies for whatever reason (too many confounding factors, limited sample size), then combining several studies dealing with the same subject can ameliorate the shortcomings of the single studies by having a much larger sample size. Confounding factors get “washed out” with very large numbers, and the statistical power in increased.

What Dr. Boaz and her colleagues did is select four studies that lent themselves to meta-analysis. Two tested low-carbohydrate diets and two low-fat diets.


And the results?

Results were pretty discouraging, but not altogether surprising. The manipulation of macronutrient composition (fats or carbohydrates) did not seem to have significant effects on weight loss in the long run. Furthermore, both low-fat and low-carbohydrate diets were associated with poor adherence and high attrition rates.

Why aren’t we surprised? Even beyond the common experience of the futility of such diets, we now know the scientific basis for it. As we wrote in the November 5, 2011 post ( Weight Loss- why is it an Endless Battle?) millions of years of evolutionary adaptation is conspiring to protect us from weight loss:

“Basically, our metabolism is geared to hoard calories, and it makes perfect sense. Not just us humans, but also our evolutionary cousins the apes, and our common ancestors the monkeys faced the same dilemma: how do you survive in an environment where food supply is not assured from one day to the other, and most of it is of low caloric density? The answer: you conserve, you save for a rainy day. Indeed, the metabolically-prudent individuals who were equipped with a set of hormones that favor calorie storage had a selective advantage over the metabolically- profligate individuals whose metabolism adhered to the siren song of “eat and drink, for tomorrow we die”.


How does the body ”protect” itself from weight loss?

Among the most important hormones that regulate appetite are leptin, ghrelin, peptide YY, amylin and cholecystokinin (CCK). These hormones, in the aggregate, have one mission: homeostasis. That means preserving the physiological status quo. If caloric intake is reduced their effect would be to conserve as many calories as possible for the proverbial rainy day. It is easy to see the importance of this system in circumstances where the next meal is not guaranteed when wide fluctuations in dietary intake are the rule, rather than the exception.

Even when this hormonal reality was understood, there was the hope that with prolonged dieting these hormones will finally adjust to the new metabolic reality and send their signals to the brain with less urgency, so to speak. The hope was that leptin will eventually come back up, ghrelin will stay down, and so on, as the lower caloric intake persists over weeks and months.

No such luck: the NEJM paper titled Long-Term Persistence of Hormonal Adaptations to Weight Loss (New England Journal of Medicine, Oct.27, 2011) showed that the appetite hormones maintained their original, pre-dieting levels, for at least 12 months (the length of the study). Is it any wonder that dieters describe their frustrating experience as a never-ending battle?


What’s next?

First, enough with those studies comparing different diets. This is beating a dead horse and a colossal waste of time and money.

Second, our physiology still obeys the laws of physics. To lose weight we need to spend more calories than we take in. As we wrote in our November 5 post:

  1. You need to lose more calories than you take in. You can guess where I am going: exercise. I can’t emphasize its importance.  Not only is exercise heart-healthy, it is diet -friendly as well. There are some fringe benefits that are not restricted to calorie-loss. Exercise releases endorphins and enkephalin, as well as endocannabinoids. The first two are the natural equivalent of morphine, the third has the same effect as marijuana. No wonder regular exercisers report a sense of well-being,  even euphoria when they exercise. And happier people tend to eat less, to boot.
  2. Most controlled studies find that the most effective diets have a high protein and a low glycemic- index content. And you don’t  have to avoid all carbohydrates – such punishment is unnecessary. You can fill your low glycemic- index portion with fruits, vegetables, and fiber.
  3. Get frequent and continuous feedback. You can do it with an online support group, a buddy, or your bathroom scale. Daily weigh
    yourself, and if you see the beginnings of an upward creep- don’t delay,  bring the weight down ASAP. The longer you wait, the tougher it will get.

Bottom line: it is what it is –you can’t change millions of years of natural selection. But you can change your lifestyle. After a while, it becomes second nature, and a happy one, too

Dov Michaeli, MD, PhD
Dov Michaeli, MD, PhD loves to write about the brain and human behavior as well as translate complicated basic science concepts into entertainment for the rest of us. He was a professor at the University of California San Francisco before leaving to enter the world of biotech. He served as the Chief Medical Officer of biotech companies, including Aphton Corporation. He also founded and served as the CEO of Madah Medica, an early stage biotech company developing products to improve post-surgical pain control. He is now retired and enjoys working out, following the stock market, travelling the world, and, of course, writing for TDWI.


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.