Losing weight is easy — keeping it off is the hard part. Why is regaining weight the most likely outcome of dieting? It is such a simple question, but one that continues to stump obesity researchers.
One of the most common explanations given for weight regain is a drop in our metabolism. The idea has merit, but only reveals part of the picture. Measuring changes in metabolism is easy compared with getting an accurate fix on how much food a person is consuming, as our eating habits can change from day to day. Tracking what and how much a person eats in the free-living world has proven a tough nut for scientists to crack.
Diet vs pills
A new way of looking at changes in eating patterns after weight loss was needed, and a novel way to do this arose from a clinical trial with a new drug for treating diabetes. The drug, called canagliflozin, works by making the kidneys excrete excess glucose, which results in lower blood-sugar levels. And weight loss turned out to be a favourable side effect.
In the trial, 153 people with type 2 diabetes took the drug for a year, while a comparison group of 89 people took a placebo pill. Both groups lost weight, but it was around 3kg in the drug-treatment group and just 1kg in the placebo group.
The surprising results
The slightly higher weight loss among those taking the drug was not surprising — the real mystery was why this group didn’t lose more weight.
Lab tests estimated the amount of energy lost in the urine from excreted glucose was roughly 1500 kilojoules (360cal) per day. That’s a lot of kilojoules being excreted by the body — so why did weight loss plateau?
To explain the plateau, the research team burrowed into mathematical models of how body weight and energy intake are related, and the answer they came up with was, quite simply, ‘appetite’.
Driven by hunger
The problem was, people in the drug-treatment group were hungrier and this drove them to eat around 420 kilojoules (100cal) extra each day for every kilogram of weight they shed. In fact, the more weight they lost, the more they compensated by eating. This surge in appetite that drives weight regain is three times stronger than the effect of a slower metabolism. Add the two together and it appears almost inevitable that, for most people, the weight will creep back on.
Making sense of it all
The reality is, regaining weight has little to do with poor self-control. Our bodies are primed to fight against weight loss. We can ignore hunger cues for a while, but they will persist longer than our willpower. A better approach is to take the focus off ‘the best way to lose weight’ and, instead, look for positive lifestyle changes which emphasise a healthy relationship with food and, generally, healthier eating habits that we can maintain for life.
Did you know? 80 per cent of people who lose weight put it back on over time.