Our Brains Control Why We Eat – But You’re Much Smarter

Dr. Sears' Blog: Our Brains Control Why We Eat – But You’re Much Smarter

Do you ever eat a big meal and feel stuffed, yet still put down a dessert high in fat and sugar? Do you ever over-eat to the point that you need to unbuckle your belt a notch, or even unbutton your pants?

There are multiple systems within your body that are circuited to the brain that interact to determine your weight loss and gain: your energy-balance system, and your appetite control center. While these interactions may seem out of your control, with the right mindset, they can be managed, and even controlled.

Your body weight is predetermined by an internal system

Each person has an energy-balance system within their body that constantly measures incoming hormonal inputs from their gut and blood to determine whether or not they should eat. This system is called the hypothalamus. The hypothalamus is the foundation for determining a set-point for body weight.

If your weight goes up or down beyond your genetically defined range, your brain tells you whether or not you should eat. This makes it difficult to maintain significant weight loss, because you’re constantly fighting against your own brain.

Under normal circumstances, this energy-balance system is 99.5% precise to maintain a set-point for your weight, and appears to be genetically controlled. This is why the average American can eat close to 750,000 calories per year and still gain less than a pound of weight (usually fat). It’s all predetermined.

Is the thermostat on your weight out of control?

Consider your hypothalamus to be a high-tech biological weight control thermostat. It works by constantly monitoring your gut and blood hormone levels, including leptin and insulin. Leptin comes from the fat cells to indicate if you have enough stored fat for a future rainy day. Insulin comes from the pancreas to indicate if you have enough blood glucose to supply the brain right now.

Under normal circumstances, these two hormones reach the brain and interact with their receptors in the hypothalamus to stop hunger.

But what if conditions are not normal? What if you have developed resistance to both insulin and leptin in the hypothalamus?

Although your blood levels might be normal, the information may not reach the interior of the target cells in the hypothalamus. As far as the brain is concerned, the compromised insulin and leptin hormonal signals indicates to your energy-balance system to keep on eating (especially fat and carbs) because both your short-term (low blood sugar) and long-term (lack of sufficient body fat) survival may be at risk. The hypothalamus responds to these attenuated messages from leptin and insulin by generating hunger signals causing you eat more.

So what happens when you go on a diet? The levels of insulin and leptin drop in the blood, and you are constantly hungry. Why? Because your hypothalamus thinks your survival may be compromised and increasing the strength of the hunger signals.

Controlling your weight doesn’t need to be heavy

The most common way to solve this weight-loss induced constant hunger problem is to increase insulin and leptin levels in the blood by eating more carbohydrates and fat. This will cause both hormone levels to rise. Eventually the increased leptin and insulin levels in the blood become high enough so the hormonal signals finally overcome the hormone resistance in the hypothalamus and you stop having consistent hunger. Unfortunately, in the process the lost weight starts to return.

This helps explain why there is such a low percentage of long-term success with diet-induced weight loss. Much of what we attribute to lack of willpower in people who regain this lost weight is really due to disturbances in hormonal communication.

Recognizing that your internal energy-balance system is unique, there still remains an elegant approach to reduce hormone resistance in your hypothalamus. Of course, it is only possible if you know what causes insulin and leptin resistance in the first place.

Increased cellular inflammation in the hypothalamus makes it increasingly unresponsive to both insulin and leptin. Although insulin and leptin are structurally different hormones and have different receptors, they use essentially the same internal signaling pathways. This means that cellular inflammation in the hypothalamus will disrupt both signaling pathways. Unless you reduce cellular inflammation in the hypothalamus, your only option to avoid constant hunger is to continue eating sugar and fat. This will increase the levels of insulin and leptin in the blood so their signals reach the appetite control center in the hypothalamus.

Your brain rewards you. Bonus – you get to live!

The dopamine reward system is your brain also controls hunger. Whereas the energy-balance system in the hypothalamus is necessary for survival, the dopamine reward system in a nearby section (ventral tegmental area or VAT) of the brain determines the desirability of eating. If there is no reward for doing something important for survival (like sex or eating), then why do it? The dopamine reward system reinforces habits that are necessary for the survival of any species (like sex is good, food is good). It is the same dopamine reward system that can be hijacked by addictive drugs and behaviors.

What if you had a significant deficiency of dopamine production in your brain? Studies with genetically modified mice that don’t feel rewarded after eating do not eat. As a result, they die soon after birth. That’s why the dopamine reward system is critical. It establishes that the habit of eating is good for survival.

Insulin resistance also affects dopamine-producing cells. Therefore, if you have insulin resistance in the energy-balance system of the hypothalamus, you also have dopamine resistance. This inhibits the release of adequate levels of dopamine to give you pleasure from eating the food.

You have two choices to get adequate pleasure out of eating. Either you can increase your intake of palatable foods high in fat and sugar by having dessert at the end of a meal, or by binge eating. Or better idea: you can reduce insulin resistance so that eating less food actually generates more pleasure. This occurs through increased dopamine release.

Avoid overeating: Sync your energy-balance system and appetite control center

The reason you overeat is because you need an appropriate interaction between the energy-survival system (“I eat to live”) as well as the hedonic dopamine reward system (“I love to eat”). Optimal dietary control only happens if you lower hormone resistance in the hypothalamus. Since insulin and leptin resistance are similar in their pathways inside the cell, anyone with insulin resistance is likely to have leptin resistance.

If you have diabetes or metabolic syndrome (i.e., pre-diabetes), you definitely have insulin resistance, and not surprisingly, you are constantly hungry. According to the American Diabetes Association, more than 110 million Americans have either pre-diabetes or diabetes. However, about 16% of normal-weight Americans also have insulin resistance.

How do you know if you have insulin resistance? Take my Insulin Resistance Quiz. This quick questionnaire will provide your personal Insulin Resistance Score, along with personalized dietary recommendations. If these dietary recommendations are working, you will not be hungry or fatigued for five hours after meals.

The secret for a truly healthy diet is to maintain lack of hunger and fatigue for the rest of your life.


  • Sears, Barry. “Gaining it Back: The Science behind The Biggest Loser’s Failure.” Dr. Sear’s Blog. (2016).
  • Davis JF, Choi DL and Benoit S. “Insulin, leptin, and reward.” Trends Endocrin Metab 21:68-74 (2009).
  • Daws LC, Avison MJ, Robertson SD, Niswender KD, Galli A, and Saunders C. “Insulin signaling and addiction.” Neuropharmacology 61:1123-1128 (2011).
  • Sotak BN, Hnasko TS, Robinson S, Kremer EJ, and Palmiter RD. “Dysregulation of dopamine signaling in the dorsal striatum inhibits feeding.” Brain Res 1061:88-96 (2005).
  • McLaughlin T, Allison G, Abbasi F, Lamendola C, and Reaven G. “Prevalence of insulin resistance and associated cardiovascular disease risk factors among normal weight, overweight, and obese individuals.” Metabolism 53:495-439 (2004).

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About Dr. Barry Sears

Dr. Barry Sears is a leading authority on the impact of the diet on hormonal response, genetic expression, and inflammation. A former research scientist at the Boston University School of Medicine and the Massachusetts Institute of Technology, Dr. Sears has dedicated his research efforts over the past 45 years to the study of lipids. He has published 40 scientific articles and holds 14 U.S. patents in the areas of intravenous drug delivery systems and hormonal regulation for the treatment of cardiovascular disease. He has also written 14 books, including the New York Times #1 best-seller "The Zone". His books have sold more than 6 million copies in the U.S. and have been translated into 22 different languages.


  1. protein purification

    When we are young, parents let us eat a variety of food to avoid malnutrition. However, this approach is not entirely correct. If we refuse to eat certain foods, it is likely that we do not lack this material in the body.

  2. Dr. Arcadio P. Sincero

    Dr. Sears,

    You mentioned in many of your Zone books that high protein, low carbohydrate ketogenic diet produces abnormal chemicals called ketone bodies. The body has no use for these ketone bodies that “it tries like mad to get rid of them through increased urination”.

    However, I’ve read some books on metabolism such as that of J. G. Salway that the brain, muscles and kidneys (except the liver) can use ketone bodies.

    I may be reading this metabolism books wrong; however, if I am reading them correctly, could you explain the discrepancy. Thank you very much.

    • Barry Sears

      Ketones are a back-up system to generate ATP, especially for the brain, if there are insufficient levels of blood glucose for optimal brain function. The brain can’t use fatty acids for ATP because it would then start digesting itself. Even under conditions of complete starvation blood glucose levels do not go to zero as the body will start converting protein into glucose. Studies done at Harvard Medical School indicate that a ketogenic diet also increases the level of cortisol and lowers T3 levels. Although the brain and other organs can use ketone bodies as a potential energy source, this doesn’t mean that they are ideal subtrate for ATP production.

  3. Mark McGinn

    Dr. Sears, studies out there in mice are looking at gut microbes and links to multiple conditions like obesity, auto-immune diseases and even autism.

    Are other studies pointing to unresolved, chronic inflammation, that is disrupting the signaling pathway of hormones and neurotransmitters, as an underlying cause of chronic diseases ?

    And could the link to gut microbes be coming from inflammation produced by out of balance gut microbes & leaky gut ?

    • Barry Sears

      The answer is yes and will be explained in far greater detail in my new book, The Skin Zone, coming out in May 2017.

  4. S. Healy

    Do you have any thoughts on intermittent fasting? I have been doing the 5/2 system, where two days are limited to 500 calories, 5 days a Zone type eating approach (albeit more calories than Zone recommends). Blood parameters and weight loss have been very positive.

    • Barry Sears

      The Zone Diet is a calorie-restricted diet without hunger or fatigue. Here are two important keys for long-term dietary success: (1) you have to restrict calories and (2) you are not going to be successful if you are hungry or fatigued. The number of calories consumed on the Zone Diet and any type of intermittent fasting program are probably the same. However, it is very easy on the an intermittent fasting program to see your calories increase on your Porky Pig days even if you are eating Zone meals. If you are not following Zone dietary principles, then increased calorie intake almost guaranteed after a few months. Following the Zone Diet puts you on auto-pilot so you don’t have to invoke constant willpower to maintain the least amount of calorie intake without hunger or fatigue.

  5. Adriana vink

    Thanks Barry I continue to do well and healthy and although 83 years of age I have no aches and pain and not overweight and besides your omega-3 and maqui supplements I do not take any medicines just a quarter of a low dose baby asperity!!! Adriana Vink

    • Barry Sears

      Medicine is not that complicated if you are treating food like drug to be taken at the right dose and at the right time.

  6. George Visger

    Thank you Barry for your lifetime of work to make people healthier. And I’d like to thank you personally for all you have done for me to help me recover from my 9 NFL caused brain surgeries. Your Omegas and anti oxidants, and directives have turned my life around.

  7. Mark McGinn

    another great article Barry, it’s never just one thing, once a person knows how to control inflammation then there is hope, The Zone diet approach


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