Losing weight and keeping it off long-term is difficult, according to numerous studies. It's estimated that more than 80% of people who lose a lot of weight gain it back within 5 years.
But the problem usually isn't about lacking the willpower to make lifestyle changes like eating healthier, reducing calories, and exercising more. The truth is our bodies are biologically programmed to hold onto fat thanks to evolution.
"We evolved not to lose weight intentionally," says Harvard paleoanthropologist Daniel Lieberman. He explains that humans need more fat than most mammals - even thin people have 3-4 times the fat percentage of other mammals. Fat helped our ancestors survive:
Big brains use tons of energy - 20% of our metabolism goes to our brains. Babies are born very fat to power their brain development
Fat is storable energy that fueled our ancestors' bodies to find food and keep their brains working so they stayed healthy enough to reproduce
So humans evolved to store fat easily and hold onto it at all costs for future energy needs. We were never meant to lose weight on purpose.
Of course, most of us don't need to fuel our bodies to walk miles hunting food or escape predators. But our biology is still adapted to an environment and lifestyle different than today. This "mismatch" means conditions like obesity and related health issues are much more common now.
"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," says Lieberman.
When it comes to weight loss and body image, Lieberman suggests considering these 5 evolutionary perspectives:
1. Not all humans are meant to be thin. We need more fat than most mammals. Even thin people have 15-25% body fat.
2. Fat equals success. It provides energy to fuel our big brains, reproduction, and active lifestyles. But too much belly fat can cause health problems.
3. Small weight fluctuations are normal. Our ancestor's weight cycled based on food availability. Short-term changes are often just water weight.
4. Losing weight is extremely hard. Our bodies evolved to store fat efficiently, not diet. Weight loss triggers "starvation responses" that slow metabolism and increase cravings.
5. Dieting and exercise serve different roles. You can lose more weight quickly by dieting than exercising. But exercise prevents regaining weight plus has other major health benefits.
The mismatch between our Stone Age bodies and modern obesogenic environments make it hard to stay slim. But understanding the evolutionary science behind weight loss resistance can help us be more compassionate, both toward ourselves and others who struggle with their weight.