The causes of weight gain are often debated, with conflicting opinions on the roles of carbohydrates, sugar, and calories. This article will clarify the science behind weight gain, focusing on the role of energy balance and the brain.
The calories in versus calories out model, which states that weight change is determined by the difference between energy intake and expenditure, is supported by scientific evidence. Studies using accurate measurement methods like respirometry show that calorie intake increases with body fatness. This isn’t simply due to increased fat mass, but also due to the accompanying increase in lean mass, which requires more energy. Restricting calorie intake leads to fat loss in individuals with obesity, demonstrating the causal relationship between calorie intake and body fatness.
While macronutrient composition (carbohydrates, fats, and protein) can influence calorie intake in free-living situations, studies where calories are tightly controlled show minimal differences in fat gain between high-carbohydrate and high-fat diets. A meta-analysis of metabolic ward studies by Kevin Hall confirmed this, finding negligible differences in fat gain when calories were matched.
While protein’s thermic effect is significant, it doesn’t seem to substantially impact energy balance or body fatness in controlled studies. However, in real-world scenarios, higher protein intake can improve satiety, thereby reducing calorie intake.
Individual responses to different diets vary considerably. While average results may be similar between low-carbohydrate and low-fat diets, some individuals may respond better to one approach over the other. This suggests a role for personalized approaches to weight management.
Genetic factors play a substantial role in weight gain susceptibility. Studies on identical twins demonstrate that while twins gain similar amounts of weight in similar locations when overfed, there is significant variability between twin pairs. This indicates a genetic predisposition to how individuals respond to calorie excess.
The brain plays a critical role in regulating body fatness. It acts like a thermostat, with feedback loops that respond to changes in energy balance. When body fat decreases, a “starvation response” kicks in, increasing hunger, cravings, and food cue reactivity while decreasing metabolic rate. Conversely, overeating triggers a compensatory response to protect against fat gain, although this response is less effective and more variable between individuals.
Non-exercise activity thermogenesis (NEAT), or fidgeting, contributes to energy expenditure. Some individuals subconsciously increase NEAT in response to overfeeding, burning off excess calories. While this response is largely subconscious, conscious efforts to increase physical activity can also contribute to energy expenditure.
Brain function contributes significantly to weight gain susceptibility. Genetic variations affecting brain circuits involved in appetite, food reward, executive control, and body fat setpoint can influence an individual’s predisposition to weight gain.
Alt text: Diagram illustrating brain regions involved in appetite regulation.
While sugar often receives blame for the obesity epidemic, the relationship is more complex. Sugar consumption has decreased in many countries while obesity rates have risen, suggesting that sugar isn’t the sole driver. While excessive sugar intake can contribute to liver insulin resistance and metabolic issues, its primary impact on weight gain is likely through its palatability, which increases calorie intake.
Foods combining carbohydrates and fats, especially with added salt and glutamate, are highly palatable and can trigger dopamine release in the brain, leading to cravings and addiction-like behaviors. Chocolate, pizza, ice cream, and french fries are common examples.
For individuals predisposed to weight gain, managing the food environment is crucial. Removing tempting foods from sight and keeping readily available foods focused on whole, unrefined options can help regulate calorie intake and reduce cravings.
Alt text: Image depicting a healthy food environment with whole, unrefined foods.
Other helpful strategies include adopting a whole-food diet emphasizing unrefined, lower-calorie density foods, increasing protein intake, engaging in regular physical activity, prioritizing adequate sleep, and managing stress levels. If these strategies aren’t sufficient, consider reducing carbohydrate or fat intake. While tracking calories and macronutrients can be helpful for some, it’s not essential for everyone. Focusing on creating a supportive food environment and lifestyle can be a more sustainable approach for many.
