PETER ROGERS, THE CONVERSATION 11 JUNE 2020
So you've done everything you're supposed to. You're eating in a calorie deficit, are exercising a few times a week, and are getting close to your weight loss goal. And then you hit a plateau with only a few pounds to lose – and they just won't seem to budge. It's long been a complaint that those last five pounds can often be the hardest to lose. And the answer to why this is the case reveals a lot about the dynamic relationship between body weight and appetite (what we feel when we say we're "hungry"), and about how, as humans, we're almost always "ready to eat". When dieting to lose weight, there are two basic reasons why weight loss typically slows down over time. The first reason is that calorie (energy) expenditure decreases with weight loss. This "slowed metabolism" happens because fewer calories are required to maintain and move a lighter body. The second reason why losing weight becomes progressively difficult is that weight loss is accompanied by an increase in appetite. The hormone leptin tells our brain how much fat is stored in our body. When we have more fat stored, leptin increases and reduces appetite. But when we lose body fat, the leptin "brake" on our appetite is partly released, making us a little more hungry. Ready to eat Left unchecked, signals from our stomach leave us vulnerable to overeating. This is because our stomach has the capacity to accommodate more calories than we expend. For example, a recent study found that when participants were served pizza for lunch and invited to eat until they felt "comfortably full", they ate 1,580 kcal. When they were asked to eat as much as they could, they ate twice that amount – their daily calorie requirement in a single meal. This shows that we are almost always ready to eat – and capable of eating beyond a level of comfortable fullness. So we're prone to overeat high-calorie foods for two reasons: they're less filling per calorie, and they're more delicious (and pleasurable) to eat. But recent research shows that high-calorie foods often don't give us that much more pleasure when we eat them. This should make it possible to reduce calorie intake without significantly affecting pleasure.
round a point that is a balance between the lure of the foods that we include in our diet, our eating restraint, and the energy we expend in physical activity. We can change all three, although choosing foods with lower energy density may be an especially effective strategy to reduce weight. And for maintaining that healthier weight, it is worth keeping in mind that lighter bodies require fewer calories. Peter Rogers, Professor of Biological Psychology, University of Bristol