Weight loss is not a math equation

We humans are much more dynamic and complex than calories in minus calories out.

Results from a study released last week provided new evidence that there is no one-size-fits-all approach to weight loss. There is no math equation that applies to everyone trying to lose weight. And while we’ve long known that some people can lose more weight than others, this most recent study helps us know why.

In it, 12 obese men and women were studied over 6 weeks. The subjects stayed in a comfy metal chamber that determined their metabolic rates by measuring the amount of oxygen they consumed. Consuming more oxygen equals burning more calories, both during exercise and at rest. Over the course of the 6 weeks, each subject was fed just 50% of their daily energy requirement. They weren’t able to exercise, so their weight loss was a result of their diet.

Since each subject consumed the same relative amount of calories, should they all have lost the same percentage of body weight?


They all lost different amounts of weight. Just like what we see outside of a laboratory. Why?

In this study, researchers found that the subjects that lost the least weight during the six-week fast were those whose metabolisms decreased the most.

It’s not because some people are “lazy” or other people are just highly motivated and “adherent” to their program; there are real physiological differences in how each individual burns calories.

As we lose weight, our bodies don’t burn as many calories; they start to conserve energy, both at rest and during exercise. And the faster the weight comes off, the more your body will slow down metabolically.

But, as this recent study confirms, how much weight is lost and how much a metabolism slows down varies widely from individual to individual. A 50% reduction in calories does not equal a 50% reduction in metabolic rate for everyone. For some it may be a 5% reduction in metabolic rate (these people will lose more weight), and for others it may be much more.

In physiology, this is called the individuality principle. Or, as I like to call it, the snowflake principle: we are all made of the same stuff, but each of us is unique (just like no two snowflakes are the same, get it?). While physiological responses are predictable, precise adaptations vary among individuals.

The authors of this study point to a “thrifty metabolic gene” that they didn’t actually test for. But it’s probably more complex than that. There may be gender differences in how much weight we can lose. There may psychological differences in how much we spontaneously move, which over the long term can have a huge influence on weight loss. And there are definitely differences in how much exercise we think will cause weight loss.

If athletes that are completing the same training program can have variable results in terms of performance, why would we expect weight loss to be any different? Why do we keep telling people that energy balance is a scale of consumption and use?

Energy balance is much more dynamic and complex than just two parts of an equation. In reality, energy intake influences energy output, and vice-versa. We know that when you cut energy intake, your resting metabolism slows down. But do you also have as much energy to exercise? And when you exercise, do you get hungry afterwards? Probably; that’s a normal response that’s happening in your brain stem.

Successful, long-term weight loss will always occur with lifestyle changes in diet and exercise. But weight loss is complicated! Knowing exactly how much diet and how much exercise is the right amount will depend on how your body adapts to those changes. And the only way you will know for sure how your body is changing is by having a goal, a plan, and the data to match.

Have a question about energy balance? Give us a shout! And collect some data on yourself!

photo credit: Alan Cleaver/Flickr