Obesity is a Disease

The vast majority of the lay public, including many people who are significantly overweight, many physicians, and mid-level healthcare providers mistakenly believe that obesity occurs when a person lacks “self control.” 

Medical science has demonstrated that obesity is a disease which, although not fully understood, is a result of the body’s abnormal regulation of a person’s weight.

The failure of the general public to understand that obesity is a disease results in many people being subjected to “fat” discrimination, developing low self-esteem, and/or depression/anxiety.

The failure of the medical profession to understand that obesity is a disease results in a delay in implementing objectively effective therapies and the development of avoidable medical/psychiatric problems and the reduction in longevity.

Obesity is a Disease

Obesity is a disease just like hypothyroid (an underactive or low thyroid) and Type 1 Diabetes (childhood diabetes) are diseases.  

People whose body’s produce too little thyroid hormone who are not treated with thyroid hormone will gain a large amount of weight (even if they eat properly), develop many health problems, and die prematurely. When treated with thyroid hormone, they will live a normal life.

People whose body’s produce no insulin have Type 1 Diabetes. If they are not given the insulin their body needs, they will have extraordinarily high blood sugars, even if they exercise and eat properly. Without being insulin, they will develop severe medical complications and die. When treated with insulin, they can live a normal life.

Today we know that obesity is a disease just like Type 1 Diabetes and Hypothyroidism are diseases. While the latter two disease are well understood from a physiologic perspective, obesity is a far more complicated disease, about which we still have much to learn.

Weight Set-Point

Every person has a “set point” for their resting respiration (breathing) rate and resting heart rate. This is the rate when a person is at rest and not thinking about these parameters, 

Every person also has a “weight set-point,” which is the weight the body wants to maintain. 

For most adults in America, the “weight set-point” increases at a rate of about 1-2 pounds per year. 

For people who have the disease of obesity, their weight set-point is set at an unhealthy and high level, and the individual’s physiology will work against them to maintain this abnormally high weight in the face of dieting and exercise.

What Do We Know About the Weight Set-Point

  1. People who have the disease of obesity do not feel satiated until they have eaten more food than thinner people. This is because obesity causes their body to produce a lower amount of “satiety” hormones (chemicals that tell us when we should stop eating) than are produced in the body of thinner people. The subcortical areas of our brain regulates how much food we eat and this structure appears to malfunction in people who are overweight or obese. Telling someone to “just eat less food for the rest of your life” is like telling somebody “I want you to permanently breathe slower for the rest of your life.” Neither can be done indefinitely.
  1. Some people who have the disease of obesity have a different gut bacteria population than non-obese people; this may be a contributing factor to obesity. For a long time it has been known that children who are repeatedly treated with antibiotics for ear infections are more likely to develop obesity later in life. Maybe the repeated administration of antibiotics to kids alters their gut bacteria and this predisposes them to developing obesity.
  1. When a person loses a significant amount of weight, the body alters the way it functions so as to regain the lost weight. It begins to work more efficiently, the body needs fewer calories for organ function, to maintain the body temperature, and for muscle function. The body then uses these “saved” calories to increase the adipocyte (fat cell) mass and this pushes the individual’s weight back up to their weight set-point.
  1. Weight gain which last for a long time (months-years?) increases an individual’s weight set-point to the new, higher weight. Unfortunately weight loss does not lower our weight set-point. The system is only designed to ratchet up the weight set-point. From an evolutionary perspective, this makes sense; but it works against our health interests when we live in an environment which has plenty of food.
  1. Eating highly processed foods cause a person to eat more calories when compared to eating unprocessed foods, even when the foods are equally appetizing. This likely works through the mechanism discussed in (paragraph 1, above). I refer to these highly processed foods as “trigger foods,” once you start eating them, they trigger a chemical reaction in your brain so that you do not stop eating them until they are gone.
  1. When animals eat highly processed, calorie dense foods it causes changes in the structure of a section of the brain (microglial cells and astroctyes in the arcuate nucleus of the hypothalamus) which is responsible for the regulation of caloric intake and the weight set-point. These structural changes are then followed by an increase in the weight of the animal, including humans. This process is referred to as “hypothalamic gliosis.” Unfortunately subsequent weight loss does not cause the altered the brain structure to revert to normal.

The net effect of these processes is that the vast majority of people who attempt to lose weight ultimately regain some or all of the previously lost weight as their efforts to lose weight did not address the underlying cause of the obesity.

How Should the Disease of Obesity be Treated


It is not possible to predict which diet will be the most effective for an individual, however this may be about to change as a result of “big data.” 

At this time, the best diet is the diet which works best for the individual, for some this will be a low carbohydrate diet and for others it will be a low fat diet.

Time Restricted Eating / Intermittent Fasting

Time Restricted Eating / Intermittent Fasting is a form of dieting in which a person restricts their caloric intake to an “eating window” of, say 6, 8 or 10 hours. If someone adopted an 8 hour eating window, then they would consume all of their calories between, say noon and 8PM.  Outside of the eating window, they may ingest only water, black coffee and tea but nothing containing any calories. This type of diet may be effective and easier than counting calories for some people.

Avoidance of Highly Processed Foods

All people, whether normal weight, over-weight, or obese should avoid eating highly processed food as these types of food are clearly associated with weight gain, as discussed above.

Avoidance of Trigger Foods

People should avoid “trigger foods,” which are those foods that once a person starts eating them they do not stop eating until the food is gone. These foods should be removed from the home. Different people will have different trigger foods.

All people who are trying to lose a significant amount of weight should enroll in a structured weight loss program like Weight Watchers, as these programs have been proven to result in some weight loss.


Exercise by itself is not an effective means to induce a significant amount of weight loss, as the average weight loss is only 2-3 pounds. Despite this, some people will lose a lot of weight in response to exercise and everyone should partake in a clinically appropriate exercise routine because exercise will help to prevent weight regain and has numerous health benefits with regard to the heart, brain, bones, mental health, muscle mass, and longevity. 

Everyone should aim for a minimum of 150 minutes of clinically appropriate exercise a week, 30 minutes 5 days a week, 50 minutes three days a week, or 22 minutes every day.

If one adheres to a diet and exercise program, the “average” weight loss will be about 5-10% of body weight over 6-12 months. However some will lose no weight while others will lose a lot more weight.

While 5-10% weight loss may not sound like a lot, it is sufficient to have major health benefits. 

Of course not everyone will lose as much weight as desired, even if fully adherent to their diet and exercise program.

Weight Loss Medicines

There are several drugs which can be used to treat obesity including: phentermine/topiramate, bupropion/naltrexone, metformin, GLP1 RA (liraglutide, semaglutide, dulaglutide) and tirzepatide.

Not all people loss weight when given these medicines. A few will gain weight, many will lose some weight, and some will lose a lot of weight. At this time, we do not  know how to predict which medication will be most effective in an individual person.

The Synergy of Diet, Exercise, and Medications

When a person combines a diet, an exercise program, and takes a weight loss medication, the total weight loss will probably exceed the sum of the expected weight loss from the individual interventions. 

For example, if

  • diet results in a 10 pound weight loss and 
  • exercise induces a 3 pound weight loss and 
  • a medication causes a 15 pound weight loss, 

then the total weight loss for someone who reliably does all 3 interventions should exceed 10+3+15 pounds.  

Today, only some insurance companies will pay for weight loss medicines. 

Those insurance companies who will pay for weight loss medicines typically require a person to enrolled in an exercise program and weight loss program for at least 3 months prior to beginning a weight loss medicine. If the person does not lose at least 5% of their weight after 3 months on the weight loss medicine then they will then stop paying for additional refills.

Weight Loss Surgery or Metabolic (Bariatric) Surgery

Metabolic or bariatric surgery is the best option for inducing weight loss and for selected patients the benefits clearly exceed the risks.

Metabolic surgery increases a person’s production of the “satiety hormones,” hormones which regulate how much food we eat, and this results in people eating less food and then their weight decreases. The changes in the size of the stomach is likely a less important determinate of weight loss than the changes in a person’s hormone levels.

The expected weight loss from bariatric surgery is about 20-30% at one year and about 10-20% at 15 years, although the quality of data (IMHO) supporting long-term weight loss is somewhat problematic.

The risks of complication from bariatric surgery is similar to the risk incurred when having a gall bladder (cholecystectomy) or uterus (hysterectomy) removed. The risk of a major complication is about 2–6%.

Complications from bariatric surgery include: ulceration, gall stones, dumping syndrome, kidney stones, weight regain, bowel obstructions, low blood sugars, hernias, nutritional deficiencies (iron, calcium, B12, folate), heart burn, and maybe an increase in the incidence of suicide and alcoholism.

Benefits from bariatric surgery include: improvement/prevention/resolution of diabetes, high blood pressure, high cholesterol, reduction in heart/stroke events, reduction in diabetic complications, breast cancer, endometrial cancer, prostate cancer, pancreatic cancer, heart burn, obstructive sleep apnea, osteoarthritis, PCOS, nonalcoholic fatty liver disease, depression, eating disorders and a reduction in the death rate and increased longevity.


In patients who has the disease of obesity, the first line therapy should be a clinically appropriate exercise program in combination with the elimination of highly processed foods in favor of unprocessed foods like fruits, vegetables, fish, chicken, meat, whole grains, and nuts. It is also essential that you remove all your trigger foods from your home.

If the first line therapy does not induce the desired weight loss then the next step is to enroll in a structured weight loss program and reliably exercise 150 minutes a week.

If this too fails to engender the necessary weight loss, or a weight loss of at least 5%, then you should meet with your physician to discuss the medical and surgical treatment options.

During the treatment of obesity it is important to recognize that there is no one treatment plan that will work for ever person. Everyone is unique; thus it will take time to find your optimal treatment plan which appropriately balances cost, side effects and clinical effectiveness.

Always remember that obesity is a disease just like gout and cancer are diseases. People get diseases and most of the time and medical profession does not know why it afflicts one person and not another.

Obesity is not the result of some personal failing.

For additional information about the treatment options for obesity, visit medlineplus.gov and do a search for “Weight loss medicines” and “Weight loss surgery.”

Hayward Zwerling, M.D.

31 October 2022


Addendum 11/21/2022: Scientists Don’t Agree on What Causes Obesity, but They Know What Doesn’t. NYT 11/21/2022


Addendum 2/9/2023: What New Weight Loss Drugs Teach Us About Fat and Free Will, NYT 1/31/2023



Addendum 2/9/2023: When Weight Impacts Health from the New England Journal of Medicine Feb. 2023


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