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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A few years ago, I had a long and interesting interview with Gary Taubes, the author of “Good Calories, Bad Calories”, for a piece I wrote in the Ottawa Citizen. He had a lot of interesting things to say, but the claim that stuck with me was that “calories in minus calories out” is an overly simplistic way to think about weight loss.

To think about obesity as simply consuming more calories than you expend is naïve and even meaningless [he said]. The idea that we get fat because we overeat doesn’t tell us why we overeat. If you think about it, both overeating and sedentary behaviour are behaviours, so in effect that takes the physiological disorder of excess fat accumulation and blames it on behaviour. I quote Susan Sontag in the book, who says, basically, that anytime you blame a disease on behaviour or psychology, it just tells you how little you know about the underlying mechanisms of the disease.

That’s all very well as a philosophy, but I had trouble wrapping my head around the physiology. After all, the equation of calorie deficit is so simple, how could it be wrong? An interesting piece by Tara Parker-Pope in the New York Times is what made me think about that interview. As she writes:

Numerous scientific studies show that small caloric changes have almost no long-term effect on weight. When we skip a cookie or exercise a little more, the body’s biological and behavioral adaptations kick in, significantly reducing the caloric benefits of our effort… As a recent commentary in The Journal of the American Medical Association noted, the “small changes” theory fails to take the body’s adaptive mechanisms into account.

The article does a good job of explaining this slippery idea — it’s worth a read. It also made me go back and re-read the transcript of my interview with Taubes. Here’s another excerpt that is more clear to me now than it was to me at the time: Continue reading “Why weight loss isn’t just “calories in minus calories out””

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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Nice little nugget in the New York Times on the common claim that eating slowly makes you feel more full:

Researchers have found evidence over the years that when people wolf their food, they end up consuming more calories than they would at a slower pace. One reason is the effect of quicker ingestion on hormones.

In particular, they cite a new study in the Journal of Clinical Endocrinology & Metabolism, in which volunteers ate a bowl of ice cream in either five minutes or half an hour. Sure enough, those who ate (drank?) their ice cream in half an hour had higher levels of a pair of gut hormones that signal when you’re full, and they also felt more full.

Nothing too surprising here, but it’s always nice when you see a study that backs up folk wisdom.

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)

***

I exchanged a few e-mails last week with Canadian Running blogger Rebecca Gardiner about weight loss and exercise. It’s a hot topic these days, thanks to Matt Fitzgerald’s recent book Racing Weight and the subsequent media coverage, including this piece by Gina Kolata in the New York Times.

But if you have a little time to spare and you’re looking for a well-informed scientist’s perspective on weight loss, I’d recommend taking a look at Ross Tucker’s series at the Science of Sport blog. (Here’s part 1, part 2A, part 2B, and part 3. The series has been stalled for a few weeks, but may resume soon.) He gives a very basic explanation of the essential facts about losing weight, keeping it simple while acknowledging the complexity that lurks behind many of the statements.

In particular, he takes aim in part 3 at one of my favourite pet peeves, the “fat-burning zone” that encourages people to take it easy during cardio workouts. It’s true, he notes, that you burn about 80% fat (and 20% carbohydrate) when you exercise at low intensity, and those ratios are reversed at high intensity.

So, what you’re probably thinking is that theory that low intensity exercise is better if you want to burn fat is correct. Well, think again. It is true that at low intensity, when you walk, most of your energy comes from fat, and that as you increase the intensity, less and less comes from fat.

But what is missing in this picture is the TOTAL amount of energy.

It turns out that you burn about 50% more fat per hour at moderate intensity than you do at low intensity. So the rationale for a low-intensity fat-burning zone is spurious, unless you have time to exercise for several hours a day. But really, the most important message comes later in the same post, and I hope people don’t miss it:

[P]erhaps most significantly, the key is still to create a calorie deficit, which means that you need not worry too much about whether your energy use is coming from fat or carbs – the key is to create that deficit, because in the long run, the energy will have to be provided and you will achieve similar results regardless.

Another point Tucker makes is that it’s really hard to provide general-purpose weight-loss advice, because there are so many different things that can be going on physiologically. He advises consulting a dietitian to get personalized advice if you’re struggling to lose weight. The corollary that I’d add is that anyone who tells you they have The One True Answer to your weight-loss problems without knowing in detail about your history is kidding themselves.

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 generally try not to get too excited about mouse studies, because there’s so much uncertainty about how the results will translate to humans. Still, I was very interested in a new study on fat-burning from Australian researchers at the Garvan Institute of Medical Research. I’ve always been skeptical about the various ways people suggest trying to convince your body to burn fat rather than carbohydrates, whether it’s by keeping your heart rate in a certain zone (usually by going slower than you would otherwise go, which seems silly to me) or by taking some sort of pill.

Anyway, there’s a very good press release describing the new study and providing context, but allow me to quote the key section:

Sydney scientists have demonstrated that mice genetically altered to burn fats in preference to carbohydrates, will convert the unburned carbohydrates into stored fat anyway, and their ultimate weight and body composition will be the same as normal mice.

The research related to an enzyme called ACC2 (acetyl-CoA carboxylase) that controls whether cells burn fats or carbohydrates. There’s no doubt that this is still a very complicated area of research, so I’m certainly not claiming this is the “last word” on this topic. But it reinforces my impression that our primary focus should be on burning (or avoiding) calories, not burning fat.