Our bodies evolved during an era when food was scarce. As a result, we’re programmed to keep weight on. The brain can’t distinguish the difference between healthy weight loss and starvation, so when we start losing body fat, it senses trouble and triggers a variety of complex hormonal mechanisms designed to prevent us from losing too much.

In other words, most weight loss efforts ultimately fail not because people lack willpower, but because we’re literally battling the primitive, hardwired biology that’s meant to keep us alive.

Eating too little activates this powerful anti-starvation system—and can sabotage your efforts to lose weight or even maintain a healthy weight in a number of ways. For instance, when you start shedding pounds with most traditional diets, your metabolism slows. That’s partly because your body becomes smaller, and smaller bodies burn fewer calories. But it turns out that many people experience an additional metabolic hit that can’t be chalked up to reduced body size.  In fact, the number of calories you burn during the day can drop by as much as 40 percent—so even though you’re eating less, you might hit a weight-loss plateau or start gaining.

Eating too little can also lead to muscle loss, which not only decreases your strength and fitness but also contributes to the decline in metabolism because muscle is the tissue that utilizes the most calories.  As soon as the quantity and quality of that vibrant sinew drops, your ability to burn off the food you consume declines—and you store the excess calories as fat. Meanwhile, undereating also causes your body to start churning out more of the hormones that drive hunger and diminishes those involved in satiety.

The result: you not only feel hungrier, but also crave high-calorie foods—and when you’re eating, it takes longer for the sensation of fullness to set in, making it easier to unconsciously overeat.

Fortunately, this outcome isn’t inevitable. The Paleo diet, which has plenty of healthy protein, fat, and carbs, fills you up naturally, so you can feel satisfied with fewer calories—without crossing the line into undereating. Because the Paleo diet eliminates processed, refined carbs, most people end up eating fewer carbs overall, which can keep your insulin and blood sugar—and your hunger—in check.

Indeed, research shows that, calorie for calorie, the Paleo diet is more satisfying than either the Mediterranean diet or a low-fat diet. And because it contains a healthy amount of nutritious protein, which has all the building blocks your body needs to maintain muscle tissue, it also helps you maintain muscle mass—along with a healthy metabolic rate—when you lose weight