by Matthew W. Gillman, MD, SM

You've seen the articles: "10 ways to burn away fat!" Although most are more hype than help, new research raises the possibility that there may be ways to harness the "burn" for weight management.
Most experts say that limiting food intake is more important than increasing energy output for weight loss among obese adults. When they say energy output, they mean physical activity. But let’s not forget that energy expenditure also comes, in part, from how much heat our bodies produce when we digest and absorb the food we eat. This thermic effect of food (or diet-induced thermogenesis) typically accounts for 10% to 15% of our total energy expenditure. That’s pretty close to physical activity’s contribution; the remainder is from our basal metabolism to keep our cells humming along.

Most of us have neglected this thermic effect because we’ve believed there’s not much we can do about it. But that may not be true.

For clues, let’s look at bariatric surgery. In rats, and probably in humans too, the gastric bypass procedure ratchets up the thermic effect of food to twice normal levels. There’s not enough research yet on the newer sleeve gastrectomy procedure.

One of the most interesting things I learned a couple of weeks ago at a conference sponsored by the NIH Obesity Research Task Force is that this effect of bariatric surgery may act through major changes in the intestinal microbiota. Every one of us has about 3 times more bacterial cells in our bodies than we do native human cells, and just about all of the bacteria live in our gut. Obese mice, rats, and humans have different types of gut “flora” than do their lean counterparts. After bypass surgery in rodents, a new gut flora emerges, different from the ones in obese or naturally lean animals. Some experiments now raise the possibility that these bacteria are responsible for increased thermogenesis of ingested food and could be one of the reasons that many patients maintain weight loss well after their surgery.

Even though eating whole grains and foods with protein induce more heat production than others, claims of “fat burning foods” on the covers of magazines at the checkout counter are exaggerated. But I will be on the lookout for interventions that cause long-term change in our microbiota to enhance the thermic effect of what we eat. Perhaps we’ll figure out ways, short of bariatric surgery, to include them in conjunction with improved diet and more physical activity for longer-lasting weight loss.



Jason Block
10/16/2014 11:00am

With the recent information about the effectiveness of c diff treatment with stool transplants (http://www.nejm.org/doi/full/10.1056/NEJMoa1205037) or oral, frozen fecal microbiota (http://jama.jamanetwork.com/article.aspx?articleid=1916296), changing the microbiota appears to have a real clinical role. Perhaps we're on the cusp of some trials of the same treatment for weight loss. Your post suggests that this is a potential avenue of exploration in the future.


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