Tag: weight loss

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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There’s plenty of evidence that lack of sleep puts you at higher risk of gaining weight. A new Swedish study in the Journal of Clinicla Endocrinology and Metabolism (press release here, abstract here) offers some new insights with fMRI brain scans:

We already know that obese people tend to find food more rewarding, as indicated by brain scans of activity in the anterior cingulate cortex:

Higher activation of this brain region has been found in obese compared with normal-weight subjects when anticipating food, suggesting that the rewarding quality of food is enhanced in obesity.

The study took a dozen volunteers and kept them up all night, then looked at their brain’s response to images of food. Compared to after a normal night of sleep, they observed the same changes that you see in obesity: stronger activation of the ACC, indicating higher dopamine signalling. You want more food than normal, because food makes you feel better than it normally would. As the graph on the right shows, those with the biggest changes in brain activity also reported the biggest appetite.

A study like this, where the subjects stayed up all night, isn’t a great way of figuring out what happens in the much more common situation of, say, getting half an hour less sleep than you need, night after night for weeks or months on end. But other studies looking at appetite hormones like ghrelin and leptin suggest that the effects are similar: too little sleep = greater appetite relative to energy needs.

Of course, this leaves us with a riddle: if you have to get up an hour early to fit your workout in, do the benefits outweigh the downsides? That depends on a  lot of things, but my general sense is that exercise has so many benefits that it’s still worthwhile. The real answer, of course, is to organize your life so that you can sleep enough and get some exercise.

THANK YOU FOR VISITING SWEATSCIENCE.COM!

My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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Gina Kolata had a New York Times article last week about “brown fat” — the strange, recently discovered (in adult humans, at least) type of fat that burns lots of calories:

A new study finds that one form of it, which is turned on when people get cold, sucks fat out of the rest of the body to fuel itself. Another new study finds that a second form of brown fat can be created from ordinary white fat by exercise.

So what does this mean? No one is really sure at this point, since it’s only been a couple of years since we even realized that it existed in adult humans. Do people become obese because they lack brown fat? Or do they lose brown fat when they become obese? Or does it just seem as if obese people have less brown fat because they don’t get as cold as leaner people, so their brown fat remains dormant? We don’t know.

Still, the article made me think of a pair of posts I wrote last year (here and here) about research that linked the rise in obesity rates with a parallel rise in the typical thermostat settings in U.S. and U.K. homes. Could the warmer ambient temperatures that we expect these days have anything to do with higher rates of obesity? There are many reasons to be highly skeptical about this idea… but the fact that brown fat turns on and starts plowing through calories at colder temperatures does provide a plausible mechanism — beyond shivering — for how temperature could play a role.

Of course, researchers say, they are not blind to the implications of their work. If they could turn on brown fat in people without putting them in cold rooms or making them exercise night and day, they might have a terrific weight loss treatment. And companies are getting to work.

We don’t really need to wait for “companies to get to work,” though. We already know how to trigger brown fat without any pills: even if you don’t go for turning down the thermostat (and I don’t believe there’s anywhere near enough evidence to advise that), the other option — exercise — sounds like a pretty good idea.

THANK YOU FOR VISITING SWEATSCIENCE.COM!

My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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I’ve received a few e-mails asking what I thought of Tara Parker-Pope’s recent New York Times Magazine piece (“The Fat Trap”), which talks about how the body fights off your attempts to make it lose weight. In general, I thought it was a good piece. The basic message I came away with is the same one I hear from people like Yoni Freedhoff: if you want to lose weight — and keep it off — you have to do so using an approach that you’re prepared to maintain for the rest of your life. You can’t go on a diet for six months, lose weight, and then resume your previous diet and lifestyle (or even go halfway back to your previous diet and lifestyle!). Many (perhaps even most) people who are trying to lose weight still see it as a temporary transitional stage. That’s not how the body works, and the more widely that message is spread, the better.

Having said that, a quick note about the apparent “biological determinism” that opposes weight loss. Parker-Pope discusses some of the research by Rupert Leibel’s group at Columbia University, in which subjects are placed on carefully controlled liquid diets to make them gain or lose weight in order to observe what changes take place in their metabolism:

The research shows that the changes that occur after weight loss translate to a huge caloric disadvantage of about 250 to 400 calories… Muscle biopsies taken before, during and after weight loss show that once a person drops weight, their muscle fibers undergo a transformation, making them more like highly efficient “slow twitch” muscle fibers. A result is that after losing weight, your muscles burn 20 to 25 percent fewer calories during everyday activity and moderate aerobic exercise than those of a person who is naturally at the same weight.

I also discuss this research in (plug alert!) my book, Cardio or Weights. And the part Parker-Pope doesn’t mention is that, when you feed people extra calories, exactly the opposite adaptation takes place. In other words, after gaining weight, your muscles burn about 15 percent MORE calories during everyday activity and moderate aerobic exercise. Parker-Pope presents the research as a part of the explanation for why it’s near-impossible to lose weight — but looking at the whole picture, that would mean that it should be impossible to gain weight in the first place! Sure, the barrier is a little bigger when you’re trying to lose weight (20-25% vs. 15%). But the point is, these changes in metabolic efficiency aren’t insurmountable barriers — otherwise no one would ever change weight at all.

THANK YOU FOR VISITING SWEATSCIENCE.COM!

My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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Another study weighs in on the question of whether fitness or fatness is a more important marker of health (abstract here, press release here). This is a nice, clear one. The researchers followed 14,345 men (with an average age of 44 at the start of the study). They did two detailed physical exams just over six years apart (on average), then followed the men for another 11 years to see which ones died, and why.

Basically, there are two variables of interest:

1. Did the men lose weight, gain weight, or stay stable between the two exams?
2. Did the men lose fitness (as measured by a maximal treadmill test), gain fitness, or stay stable?

The result: those who maintained or improved fitness were less likely to die by ~30-40% compared to those who lost fitness — even when you control for factors like BMI. Obvious and expected.

But what about weight? As you’d guess, those who gained weight were more likely (by 35-39%) to die of heart disease than those who lost weight or stayed stable. BUT if you take into account changes in fitness, then the effect of changes in weight almost disappeared. So this is further support for Stephen Blair’s argument that it’s fitness that matters, not fatness, when it comes to predicting health (and Blair is, indeed, one of the authors of this paper). As the press release puts it:

“This is good news for people who are physically active but can’t seem to lose weight,” said Duck-chul Lee, Ph.D. […] “You can worry less about your weight as long as you continue to maintain or increase your fitness levels.”

But let me add one clarification. Whenever this topic comes up, I often hear from people who say something along the lines of “See, BMI is meaningless! This proves that doctors should never even measure weight, because it doesn’t predict health.” Not quite. Let me reiterate: those who gained weight in this study were 39% more likely to die of a heart attack than those who lost weight. The reason weight gain doesn’t stay as an independent predictor of death is that those who gained weight also (on average) lost fitness, and those who lost weight also (on average) gained or maintained fitness.

So the very important message that this study reinforces is that it’s fitness that matters most. Keep exercising even if you don’t see changes in your weight, and you’ll be gaining extremely important benefits. But don’t interpret it to mean “it doesn’t matter if I gain weight, because weight is meaningless as a health marker” — because there’s a decent chance (though it’s certainly not guaranteed) that if you’re gaining weight, you’re also losing fitness.

(One final caveat: as the press release notes, 90 percent of the men were either “normal weight” or “overweight” — i.e. BMI under 30. So you can’t assume that the same lack of problems would hold true for the “obese” category with BMI over 30.)