The Diet Brain

Article at a glance

  • When starting a diet, a key component is the Set-Point Weight
  • There are two hormones that affect weight, ghrelin and leptin. Ghrelin alerts the body when it is hungry, leptin tells h body it is full.
  • The brain will try to resist new levels of weight, fat and temperature until it adjusts and creates a new Set-Pont Weight.
  • Carbohydrates can be good or bad in a diet depending on the person’s body.


    There are so many diets in the world that promote rapid weight loss. Many have other health benefits too. When on a diet, many are focused on losing weight and improving overall health, including blood pressure, and cholesterol, and boosting the immune system. Sometimes on a diet, mental health and brain health can become a bit of an afterthought. How does the brain adjust to a new diet or drastic change in eating? Can some diets improve our brain health and functions?


    Your Brains Fights Back and Resists Dieting

    When starting a new diet, something to keep in mind is the Set-Point Weight. Dr Stephan Guyenet, PhD, and author of The Hungry Brain explains that the brain naturally regulates body weight [1] and will resist any drastic weight loss or weight gain. The author of Why Diets Make Us Fat, Sandra Aamodt, PhD, agrees and explains that when the body experiences a drastic change in weight, the brain will intervene and push back to what it thinks is the correct weight. Many people prefer a different weight to their brains. 

    Guyenet uses the analogy of a thermostat to explain Set-Point Weight. A thermostat is used to measure and regulate the temperature of a home. When the home gets colder the heater kicks in, and when it gets warmer, the air conditioning turns on. In the brain, the thermostat is the hypothalamus. The hypothalamus will activate physiologic and behavioural responses to maintain your body temperature [2].


    Set-Point Weight Is Also About Fat

    The brain does not only regulate body temperature and weight but also fat. According to a registered dietitian, Dara Dirhan, there are two hormones responsible for the Set-Point Weight, ghrelin and leptin. Ghrelin senses when the body’s energy levels and energy stores are low and tells the body when it is hungry. Leptin tells the body when it is full and signals to the brain that the energy stores have been [3].

    There are levels of fat, weight and temperature where the body is at its happiest. As you lose weight and fat, your body will defend these levels and try to regain it. During weight loss the level of leptin in the bloodstream also drops. Guyenet explains this as the Starvation response [4]. This is when your brain responds to the decrease in leptin by increasing hunger levels. 


    Changing The Set-Point Weight

    Starting a new diet is never easy. In the beginning, the body may feel tired as it is not receiving the amount of calories and energy it is used to. After a few weeks the brain will adjust and find a new Set-Point Weight. Reaching a new Set-Point is not easy and is a long term goal. Jason McKeown, MD, a neurologist, explains that in order to maintain weight loss, long-term diets can influence the Set-Point range and assist the brain with adapting and being more comfortable at a new weight. [5] [6] 



    Your Brain Wants To Cheat

    The brain knows when the body is on a diet. During a diet, the Set-Point Weight is not being reached. This leads to a newfound hunger and cravings. Overeating is very easy on a diet as the leptin levels are not reached and the brain is not given cues to say the body is full. Even eating a healthy diet, but in larger portions can lead to weight gain instead of weight loss [7]. Before a diet, the body may not see the need to eat a lot or binge, but the brain on a diet will see it as necessary. Being on a diet forces the brain and the body to ignore hunger and can increase stress levels. This makes it harder to recognize natural hunger cues and regulate weight. 



     The Carb Factor

    A study by Tufts University followed 19 women in their weight loss journey. Some followed a low-calorie diet while others followed a low-carbohydrate diet. During the first week, the women in the low-carbohydrate diet had to eliminate carbohydrates from their diet completely. After the first week, women from both diets were given tests of working memory and visuospatial memory, such as “where did I leave my keys?” and memorising maps. The women with the low-carbohydrate diet did worse than the women with the low-carbohydrate diet

    Holly Taylor, Ph.D., cognitive psychologist at Tufts and co-lead investigator on the study explained that the brain is fuelled by glucose. Foods such as fruit and grains are high in carbohydrates and glucose. These glucose-rich foods are the best way to keep the brain healthy and fuelled. However, the brain cannot store more than two days’ worth of glucose. When this is depleted, glucose levels (blood sugar) drop. Although fats and protein can be used to fuel the brain they do not provide the glucose the brain needs to function properly.


    In the second week of the study, participants in the low-carbohydrate diet were able to eat small amounts of carbohydrates, such as a small piece of fruit of quarter of a slice of bread. This improved and even returned their memory and brain function back to normal. Not all diets work the same for each person. For some, a low-carbohydrate diet such as keto may decrease memory and brain function, while the same diet may improve brain function [8] for another person. Working with a licensed doctor and dietitian can help someone find the best diet for them. 



    Wrapping It Up

    Starting a new diet and improving eating and lifestyle habits can be hard. When the brain is set on a certain routine and Set-Point Weight, it will try to fight the new lifestyle. The key is to take it slow and set long term goals when dieting. This will give both the mind and body time to adjust to the new lifestyle and create a new Set-Point Weight. Eliminate or Introduce things slowly to also give the brain time to adjust. Always speak to a licensed doctor before starting a diet to know what will work best to lose weight, with minimal negative side effects on the brain and body.



    [1] Is there evidence for a set point that regulates human body weight?

    [2] What Happens To Your Brain When You Go On A Diet

    [3] This Is What Happens To Your Brain When You Go On A Diet

    [4] The science of body weight and health

    [5] The Best Way to Lose Weight and Keep It Off Long Term, According to Experts

    [6] What You Need to Know About Set Point Theory

    [7] Nutritional psychiatry: Your brain on food

    [8] Brain foods: the effects of nutrients on brain function

    [8] Is there evidence for a set point that regulates human body weight?