Q: I have tried almost every diet out there, without success. Help!
A: There are some things that everybody knows: We should all drink eight glasses of water a day. We should eat our vegetables. To lose weight, we should eat less and exercise more.
Right? Well, it seems it’s not quite as simple as all that. Recently, the New England Journal of Medicine published a much talked about paper examining some widely held beliefs about obesity and weight loss. Can you guess which ones of the following are true and which are false?
- Walking a mile a day can lead to a loss of more than 50 pounds.
- If schools reinstated physical education, a lot of fat children would lose weight.
- If you make small, long-term changes in your lifestyle, you will lose weight.
- If you set big weight-loss goals, you’ll become frustrated and set yourself up for failure.
- If you lose weight too quickly, you’re setting yourself up for failure.
If you guessed that just one or two of these are true, you’d hardly be alone. But you’d be wrong. Every one of them is false. “False and scientifically unsupported beliefs about obesity are pervasive in both scientific literature and the popular press,” say the study authors. Let’s take a look at some of them.
Myth No. 1:
Small, sustained changes in energy intake or expenditure will produce large, long-term weight changes.
To researchers, “energy” means “calories you eat,” while “expenditure” means “calories you burn.” So in other words, this myth is saying something all of us have heard a million times: Eat just a few less calories a day or walk off a few extra ones, and, over time, this will add up to a lot of lost weight.
If only that were true. The prediction that you’ll lose weight by doing these small things is based on the old rule of “one pound equals 3,500 calories.” According to this logic, if you decrease your calories over time by 3,500 calories, and/or increase the number of calories you burn by the same amount, you will lose one pound. But recent research shows that there are huge individual differences in metabolism and that our bodies adjust as we lose weight, so that we often need fewer calories than we did before.
The 3,500-calorie rule predicts that a person who burns an extra 100 calories by walking a mile a day will lose more than 50 pounds over a period of five years. In reality, the research shows that all things being equal, the amount of weight lost by walking a mile a day over five years will be more like 10 pounds.
Further—though the researchers didn’t discuss this—we now know that calories are only a part of the story. Weight gain is driven by hormones, and different kinds of foods have different effects on hormones. For example, sugar raises insulin levels. “There is no fat accumulation without the hormone insulin,” writes Robert Lustig, MD, author of Fat Chance: Beating the Odds Against Sugar, Processed Food, Obesity, and Disease. Models of weight gain that rely solely on calorie numbers ignore the profound contribution of hormones. “A calorie is not a calorie,” continues Lustig, a sentiment with which I wholly agree.
Myth No. 2:
Rapid weight loss is associated with poorer long-term weight-loss outcomes.
In my own clinical experience, a big initial drop in weight is encouraging, and as long as you don’t expect similar results every week, it can be motivating to see a significant drop on the scale early on. And more rapid and greater initial weight loss has actually been associated with lower body weight at the end of long-term follow-up. “Although it’s not clear why some obese persons have a greater initial weight loss than others do, a recommendation to lose weight more slowly might interfere with the ultimate success of weight-loss efforts,” write the researchers.
Myth No. 3:
“You have to be ready!”
I admit, this is one I totally bought into, and I’m still not convinced it’s wrong. But the researchers point to convincing data showing that when “readiness” is evaluated among folks who sign up for behavioral programs or undergo obesity surgery, where someone falls on a “readiness scale” used to determine motivation does not predict how closely someone will stick to a program or the amount of weight that will be lost. I’m a big believer in our ability to take action even when we don’t feel like it.
Myth No. 4:
P.E. classes help reduce or prevent childhood obesity.
Research shows that even when the number of days kids attend gym classes are increased, the effects on BMI (body-mass index) are inconsistent. Two large meta-analyses showed that even specialized school programs that promoted physical activity were ineffective in reducing obesity.
And that’s a good lesson for all of us. Don’t get me wrong. There’s clearly a level of physical activity that would be effective in controlling weight. But a couple of gym classes every week won’t get the job done. If you’re expecting a minimal amount of exercise to get rid of your protruding belly, you’re probably asking too much.
Myth No. 5:
A bout of sexual activity burns 100 to 300 calories.
Sorry, guys. Researchers estimate that a 154-pound man expends approximately the same number of calories during sex as by walking at a moderate pace (approximately 2.5 miles per hour). “A man in his early-to-mid-30s might expend approximately 21 calories during intercourse,” say the authors.
So where does all of this leave us? The New England Journal article is a reminder that when it comes to obesity, we still have a lot to learn. In my experience, the most sensible course of action for those wanting to lose weight is this: Cut back on the sugar, breads, and pastas. And exercise and move around as much as possible, but don’t expect miracles from doing so—diet trumps exercise in the weight-loss wars.
Jonny Bowden, PhD, CNS, aka “The Rogue Nutritionist,” is a board-certified nutritionist and the bestselling author of 13 books on health. Visit him at jonnybowden.com and follow him on Twitter @jonnybowden. Do you have a health question for Jonny? Send it to firstname.lastname@example.org. Write “Health Q&A” in the subject line.