you can’t outrun your fork. but that doesn’t mean exercise can’t help you lose weight or change your diet.

every january, millions of individuals make new year’s  resolutions  to lose weight or eat healthier, if not both. to achieve this goal, many individuals will begin strenuous exercise programs that incorporate too much exercise  too soon , leading to fitness burnout or injury.  overtraining  can actually prevent you from losing weight.

energy and exercise

the truth is that you simply cannot  exercise away  a poor diet and expect to lose weight (if that is your goal). humans are very good at conserving energy and will account for any calories burned through exercise by consuming more calories later in the day or by being  less physically active  throughout the rest of the day.

if you are looking to lose weight, the only way to do it is by  controlling your calorie intake . the best and most effective way of doing that is limiting the consumption of ultra-processed foods — typical “junk foods” and fast-food meals. even if you are not trying to lose weight, reducing ultra-processed food consumption is good for mental and physical health.

why we over-consume junk foods

we know that we shouldn’t overeat candy, cookies, cake and chips, or drink sugary sodas. diets that are high in these ultra-processed foods cause us to  gain weight . but they are just so hard to resist.

ultra-processed junk foods have been designed to be as tasty and rewarding as possible. when we are exposed to media advertisements, or actual food items (for example, chocolate bars in the checkout lane at grocery stores), brain activity in regions associated with  reward processing  increases. this reward-related brain activity results in increased food cravings and the drive to eat, even when we are not hungry.

a brain region known as the  dorsolateral prefrontal cortex (dlpfc ) helps us limit the consumption of ultra-processed foods by both decreasing activity in these reward regions to reduce food cravings and by initiating the cognitive processes needed to exert conscious control over food choices.

when using  functional brain imaging  to examine brain responses, neuroscientists have shown that increased activity in the dlpfc helps us control  food cravings  and select healthier food items by decreasing activity in the reward regions of the brain. conversely, when  activity in the dlpfc is decreased , we have a harder time resisting the temptation of appealing junk foods and will consume more snack foods.

ultra-processed junk foods have been designed to be as tasty and rewarding as possible. getty

exercise can help regulate food consumption

exercise boosts brain plasticity, which is the brain’s  ability to adapt  its functions based on new input. boosting brain plasticity makes it easier to change our habits and lifestyle. more and more evidence has shown that regular physical activity can increase  prefrontal brain function  and improve cognition.

i have shown that people consume less ultra-processed food such as chips or milk chocolate  after 20 minutes  of moderate-intensity exercise (in our study, this was a brisk walk at 5.6-6.1 kilometres per hour on a treadmill with a slight incline). research has also shown that both a single session of  high-intensity interval training  and a 12-week high-intensity aerobic exercise program can reduce preferences or appetite for high-calorie junk foods. similar effects are seen when people engage in moderate  aerobic exercise or strength training .

exercise also helps reduce stress

when people are stressed, the body releases a  hormone called cortisol , which activates what is known as the fight-or-flight response. when cortisol levels are high, the brain thinks it needs more fuel, resulting in increased cravings for sugary or salty ultra-processed foods.

participation in regular exercise or a single bout of exercise reduces perceived stress levels and  cortisol levels . exercise also helps  reduce unhealthy drink and food consumption  when people are stressed.

stress can also impact how the brain functions. research has shown that stress can result in decreased activity in the  prefrontal cortex  and increased activity in  reward regions  of the brain when looking at pictures of food. this makes it harder to resist the temptation of appealing junk foods.

what exercise is best?

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you can’t outrun your fork. but that doesn’t mean exercise can’t help you lose weight or change your diet.

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