If you think it’s hard to lose weight and keep it off, you are not alone — and you are also 100% correct. Long-term weight loss is really difficult to achieve, studies have found.
Estimates vary, but it’s believed that more than 80% of people who lose a substantial amount of weight regain it within five years.
But failure to shed pounds is often not about lacking the willpower to make important lifestyle changes, such as eating healthier, reducing calories and increasing physical activity. The dirty little secret is that our bodies are programmed by evolution to hold on to fat.
“We evolved not to lose weight intentionally,” paleoanthropologist Daniel Lieberman told CNN Chief Medical Correspondent Dr. Sanjay Gupta recently on the podcast Chasing Life. Lieberman, a professor and chair of the department of human evolutionary biology at Harvard University, studies why the human body looks and functions the way it does.
“我们进化到现在，并不会刻意去减肥，”古人类学家Daniel Lieberman在追逐生命播客中告诉CNN首席医学记者Sanjay Gupta博士。Lieberman是哈佛大学人类进化生物学系的教授兼系主任，他的研究方向是人体外观和功能的原因。
“All animals need some fat, but humans have evolved to have exceptionally high levels of fat, even thin humans,” he said. “And so we are under exceptional sort of biological pressure, always, to put it on and keep it as long as we have it, for when we need it.”
Humans are fundamentally adapted not to be happy or healthy but rather to be reproductively successful, Lieberman said. And for that, we need fat, a lot of fat — which is why Lieberman calls humans “an unusually fat species” compared with other mammals, even other primates.
“We have these big brains, which cost a huge amount of energy. … It’s 20% of our metabolism,” he said. “And a baby, when it’s born, half of its energy is paying for its brain. It needs a lot of fat. So … human babies are born very fat because they have to have that energy to make sure that they can keep their brain going.”
Lieberman said fat is storable energy. It helped early humans stay alive, powered their bodies to find food, kept their brains working and made them healthy enough to reproduce.
“It’s like money in the bank account. And so individuals who have appropriate levels of fat did better in our evolutionary history than those who didn’t,” he said. “And so we were selected to make sure that we always could put it on, because there were always times when we had to lose it.”
Lieberman said humans never evolved to lose weight deliberately.
And while our bodies haven’t really evolved from those earlier times, our environment has — and that is, what Lieberman called, a big mismatch. Nowadays, we don’t have to run from wild animals, travel long distances on foot, or hunt and gather our next meal. We can pick up a smartphone to call an Uber or Uber Eats and experience all manner of modern conveniences. As a result, many people now live with weight issues and obesity, and all of the “mismatch diseases” that stem from that.
“So mismatch diseases are defined as conditions or diseases that are more common or more severe when we live in environments for which we’re poorly or inadequately adapted,” Lieberman said, referring to our modern-day “obesogenic environment” that often contributes to weight gain.
“And so, of course, it’s hard. It’s because we evolved not to lose weight intentionally. And so, losing weight requires dieting, requires tricking your body and overcoming those adaptations — which your body’s going to fight you every, every inch of the way.”
翻译 | Romola
资料来源 | CNN