Losing and Gaining Weight…it is not as simple as calories in/calories out

Guest article by Dr. Martha Arden, part of the “Strong Mamas Fit Families” Team.

When I heard that the New England Journal of Medicine published a special article several weeks ago entitled “Myths, Presumptions, and Facts about Obesity,” I rushed to my hospital library’s website to download the article. I’ve often wondered about many of the things we think we know about obesity, the urban legends that everyone seems to believe. Is there any proof that they are they really true? The article was written by a group of 20 experts in the field from 7 different universities, funded by the National Institutes of Health, so my expectations were high.

The myths were the most surprising. The authors defined myths as common beliefs that persist despite the availability of contradicting evidence – that is, there is proof that these often-repeated truisms are false. I was very surprised that some of the things I’d always believed – and shared – weren’t true. But there were plenty of presumptions as well, where there is no evidence true or false, and more research is needed. Thankfully, there are also well-established facts that can guide us in our individual and collective efforts to be healthy and lean.

Over the next several postings, I’d like to discuss the most pertinent myths, presumptions and facts described in the article and their implications for those of us who are trying to control our weight. I think you’ll be surprised as well.

Myth 1): Small sustained changes in energy intake or expenditure will produce large, long-term weight changes.

I learned this in medical school and believed it until the day I read this report. Weight is determined by the balance of calories in vs. calories out. It’s an article of faith, passed down over the years, that a difference of 3500 calories one way or the other translates into a pound of body weight, and that small changes, made over time, will show up on our bodies.

The fact is, the 3500 rule-of-thumb was based on short-term experiments of men on very low calorie diets, and it doesn’t apply to regular life and small, long-term changes. When you think about it, this makes sense: our bodies adapt to the food we ingest and the level of activity we engage in, as our metabolism changes in response to small changes in calorie intake or expenditure. The number of calories that “makes” a pound varies depending on circumstances and how our body responds to those calories. In a study cited in the article , an increased calorie expenditure of 100 calories each day led to a 10 pound weight loss over 5 years, not the 50 pounds predicted by the 3500 calorie rule.

My experience with anorexia patients is consistent with that study: teen girls with anorexia sometimes exist for months on fewer than 500 calories a day, but their weight doesn’t just keep dropping indefinitely – their bodies struggle to adapt, lowering their temperature, heart rate and blood pressure, stopping their periods, slowing their digestion, and using a variety of other mechanisms to conserve the precious few calories they get. They still lose weight, of course, but as time passes the weight loss occurs at a much slower rate than you’d expect.

So what does the debunking of this myth mean to us? My first reaction was that this is terrible news – not only have I and other professionals been spreading misinformation, but also that our bodies don’t actually respond to changes like precision machines. It is certainly disappointing that we can’t just cut 100 calories a day and lose 50 pounds in 5 years.

On the other hand, I feel it’s liberating to know that our bodies are living and breathing, working to adapt to whatever we throw at them – we’re not machines. The disproving of this myth tells us that weight loss is harder than we may have been led to believe. There’s more to it than just cutting back a little or walking a little more. Those of us doctors and nutritionists who’ve told our patients that their lack of weight loss means they’re just not making the little changes have been wrong. Losing weight requires hard work, not just little changes. That’s a downer, but it’s good to know the truth.

Of course, it’s definitely way better to not gain excess weight in the first place, because our bodies will fight us when we try to change the status quo. The good news here is that, just as it’s hard to lose weight, our bodies also help resist gaining weight– some. I, for one, am very happy to know that if I drink an extra glass of orange juice every day for 15 years, I won’t gain 150 pounds!

So, the take-home messages from Myth #1: Our bodies resist changes in weight, so it’s far easier to maintain a normal weight beginning in youth than to lose weight later – and if we want to successfully lose weight, we have to make major changes in our diet and activity level to sustain our progress.

Reference: Casazza, et al. New England Journal of Medicine 2013; 368:446-54. “Myths, Presumptions and Facts about Obesity.”