The Evolutionary Psychology of Human Beings' Urge to Overeat
Humans evolved with a subconscious urge to overeat—especially in the wintertime.
Posted January 6, 2016
Are you struggling to lose weight by eating less as part of a 2016 New Year’s resolution? If you’re finding it difficult to resist food cravings and the urge to overindulge, you can blame your evolutionary ancestry. The human body and our subconscious mind have evolved to perceive weight gain as a success.
The ability to store body fat has aided the survival of our species for eons. Unfortunately, our bodies have also evolved with mechanisms that make it difficult for us to lose weight, as a protective measure for surviving periods of famine. Luckily, there is a way to counter the side effects of consuming too many calories. Just 45 minutes of moderate exercise most days of the week can dramatically reverse the detrimental impact of overeating.
Do you feel a subconscious urge to overeat in the wintertime?
Every autumn—when the weather gets cold and the sun sets in the late afternoon—my primal urge to overindulge in comfort foods overtakes the executive function of my prefrontal cortex. Like most people, I have a subconscious tendency to eat more in the wintertime. How about you? Do you feel the urge to overeat and tend to gain weight during winter? If so, you are not alone.
According to a new study by researchers at the University of Exeter, “There is not yet an evolutionary mechanism to help us overcome the lure of sweet, fatty, and unhealthy food and avoid becoming overweight for understandable and sensible reasons.”
The January 2016 study, “Fatness and Fitness: Exposing the Logic of Evolutionary Explanations for Obesity,” was published in Proceedings of the Royal Society B.
From an evolutionary perspective, the researchers believe that being overweight posed much less of a threat to the survival of our species than being underweight. Our subconscious drive to increase body fat stores and to gain weight is stronger in the winter, when food was typically scarce. This might help explain the double whammy of overindulging from Thanksgiving to Christmas, and why New Year's resolutions to lose weight often take Herculean effort.
In a press release, lead author Andrew Higginson, from the College of Life and Environmental Sciences at the University of Exeter, said,
"You would expect evolution to have given us the ability to realize when we have eaten enough, but instead we show little control when faced with artificial food. Because modern food today has so much sugar and flavor the urge humans have to eat it is greater than any weak evolutionary mechanism which would tell us not to.
All animals, including humans, should show seasonal effects on the urge to gain weight. Storing fat is an insurance against the risk of failing to find food, which for pre-industrial humans was most likely in winter. This suggests that New Year's Day is the worst possible time to start a new diet."
For this study, the researchers used computer modeling to predict how much fat all animals, including humans, should store. The mathematical model predicted how the percentage of fat an animal stores corresponds to food availability, and the risk of being killed by a predator when foraging for food.
Exercise Can Help Counter the Side Effects of Overeating
Regular physical exercise can protect against many of the harmful physiological effects of short-term overeating. A 2013 study from the University of Bath, “Exercise Counteracts the Effects of Short-Term Overfeeding and Reduced Physical Activity Independent of Energy Imbalance in Healthy Young Men” was published in The Journal of Physiology.
The researchers found that a daily bout of exercise triggers a wide range of physiological benefits, even if you consume thousands of calories more than you're burning. Regular exercise does a lot more than simply reduce energy surplus. In a press release, Jean-Philippe Walhin, a researcher on the study, says,
“Our research demonstrates that a short period of over consumption and reduced physical activity leads to very profound negative changes in a variety of physiological systems – but that a daily bout of exercise stops most of these negative changes from taking place.
Short-term overfeeding and reduced physical activity had a dramatic impact on the overall metabolic health of the participants and on various key genes within fat tissue – and exercise prevented these negative changes even though energy was still being stored.”
For this study, 26 healthy young men were asked to be as inactive as possible during their daily activities and everyone was asked to overeat. Then, half of the group began to exercise daily on a treadmill for 45 minutes. The non-exercising group increased their caloric intake by 50%, while the exercising group increased their caloric intake by 75%, so that everyone’s net daily energy surplus of calories in and calories out was the same.
After one week, both groups had blood insulin measurements and biopsies of fat tissue taken. The results were dramatic. The non-exercising group showed a significant unhealthy decline in their blood sugar control, and their fat cells were over-expressing genes linked to unhealthy metabolic changes and were under-expressing genes involved in well-functioning metabolism. However, the group that had been exercising for 45 minutes daily had stable blood sugar levels and their fat cells showed less "undesirable" genetic expression. Dylan Thompson, senior author of the paper, said,
“A critical feature of our experiment is that we matched the energy surplus between groups – so the exercise group consumed even more energy and were still better off at the end of the week.
If you are facing a period of over-consumption and inactivity, which is probably quite common around Christmas time, then our study shows that a daily bout of exercise will prevent many of the negative changes from taking place even though you are gaining weight.”
Conclusion: exercise can help balance surplus caloric intake year-round
Lately, the headlines have been filled with potentially confusing information about diet, exercise, and weight-loss. Does overeating make people fat, or is inactivity to blame? Common sense, and empirical data, suggest that managing your energy balance—which is the sum of your energy intake vs. energy expenditure also known as "Calories In-Calories Out"—is the key to maintaining a healthy body weight.
Eating an excessive amount of calories compared to your metabolic daily output will lead to an increase in your body weight. A calorie is the measurement of energy it takes to raise 1 gram of water 1 degree in temperature. A pound of fat equals roughly 3,500 calories. The key to sustaining a healthy weight is directly linked to matching your own metabolic rate and energy balance based on calories in and calories out.
The combination of a little willpower resisting the temptation to overindulge, and to exercise a little more can be the antidote for maintaining energy balance. Any extra energy you consume in the form of calories is always going to be stored as fat. Regular exercise is the only way you can turn this stored fat into useful energy expenditure. Luckily, very small amounts of exercise go a long way. If you aren't currently exercising regularly, why not start today?
If you'd like to read more on this topic, check out my Psychology Today blog posts,
- "Is Junk Food to Blame for the Obesity Epidemic? Yes and No."
- "Aerobic Activity vs. Strength Training: Which Burns More Fat?"
- "Very Small Amounts of Exercise Can Reap Huge Benefits"
- "Hippocrates Was Right: Walking Is the Best Medicine"
- "Will Obesity Bankrupt the United States in the Near Future?"
- "Irisin: The "Exercise Hormone" Has Powerful Health Benefits"
- "Are Sugar Substitutes Healthier Than Sugar? It’s Debatable."
- "Is Corporate Money Biasing "Science-Based" Health Experts?"
- "Digital Social Networks Can Motivate People to Exercise More"
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