This last week I’ve been immersed in the scientific literature on homeostatic regulation of body fat. As I’ve previously mentioned multiple times on the blog, hunter-gatherers and non-westernized populations are lean and healthy even when they have access to an abundance of food and engage in a minimal amount of physical activity. This suggests that our hard-wired mechanisms for regulating fat storage function properly when we live in the right ecological niche and eat “simple” diets composed of nutrient-rich whole foods. However, today we face a gene-environment mismatch in the sense that we aren’t adapted for the current ecological niche we live in, and it’s therefore no surprise that we’re seeing a steady rise in metabolic disorders such as obesity, insulin resistance, and diabetes.
Why do we overeat?
Around 30% of the population in the U.S. are now obese (1), and other affluent nations are not far behind. A general belief is that the obesity epidemic simply results from gluttony, overeating and inactivity, and that the answer is to exercise more and eat less. However, the question isn’t whether we overeat or not since it’s well established that weight gain results from an imbalance in the amount of energy that goes into the body and the amount that goes out. The question is: Why do we overeat?
The brain controls fat storage
The brain is a primary control center in our body and is responsible for regulating how much body fat we carry. In a healthy and lean human being, hormones such as leptin travel from fat cells to the brain and signal whether we should increase or decrease fat storage by adjusting hunger and energy expenditue.
However, if we disrupt the feedback mechanisms between fat cells and the brain, our body resists fat loss. The brain has essentially become resistant to the signal from leptin (leptin resistance), and since leptin production correlates with fat mass, the brain responds to a low leptin signal by increasing hunger and decreasing energy expenditure in an attempt to store more fat and boost leptin production (2).
So, even though an obese person has a lot of fat mass, the low leptin signal leads the brain to “believe” that the body is actually lean, and it therefore guards the elevated weight. If conscious calorie restriction is utilized to lose weight, the brain increases hunger and decreases body heat production and metabolic rate in an attempt to protect the body fat setpoint (3).
Conscious calorie restriction makes you lose weight because the brain’s compensatory mechanisms can only prevent so much, but the majority of people who decrease their fat mass by “starving” themselves quickly bounce back up to their starting weight when they start to eat to satiety.
To permanently shed the fat we have to figure out why the setpoint is elevated, and then design a diet that allows weight loss without conscious calorie restriction and hunger. While there are several causes of leptin resistance and elevated fat setpoint, a lot of obesity researchers now believe that food reward is a dominant factor.
Highly-rewarding food is addictive
Food can be addictive in the sense that the reward system in the brain motivates us to seek them out again and again (3,4). While refined sugar and flour in themselves aren’t especially addictive or rewarding, these ingredients are frequently used as part of products that contain a combination of several rewarding components such as fat, starch, sugar, salt, and glutamate.
These highly-palatable, engineered foods have a higher reward value than anything humans have been eating prior to the last couple of decades, and they disrupt the homeostatic system which main job is to control fat storage on a long-term basis (3,4,5).
Processed, westernized foods can also trigger leptin resistance and overeating through other mechanisms than influencing the reward system in the brain (e.g., elevating triglycerides, promoting gut dysbiosis). It remains to be seen which are the dominant factors involved, but there’s no doubt that limiting food with a high reward value is a good idea if you want to lose weight.
How to avoid overeating?
Some strategies that improve leptin sensitivity, lower the body fat setpoint, and promote weight loss:
- Eat a diet that is primarily composed of simple, whole-foods such as meat, fish, fowl, eggs, vegetables, legumes, fruits, grass-fed dairy, nuts, and berries. Properly prepared grains can also be a part of the diet if you tolerate them well.
- Take care of your microbiome by eating prebiotics and probiotics. Avoid antibiotics and don’t be too hygienic.
- Eat enough protein (>15% daily energy intake)
- Do some type of regular physical activity to improve metabolic health and increase muscle mass.
- Regularly eat fatty fish or take an omega-3 supplement.
How sugar affects the brain
I recently stumbled upon two articles (6,7) and a video that explain some of the things I’m talking about. However, bear in mind that it’s not just the biggest offenders like sugar, vegetable oils and refined grains that are problematic. For example a combination of bread, butter and cheese is relatively high in rewarding properties and is not something that should be eaten regularly if you’re trying to lose weight.