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Chapter 2: Inheriting Obesity

Jun 14, 2019


Click here to watch a Facebook LIVE replay of this discussion. 

You Will Learn

  • How much of the tendency to gain weight is hereditary?
  • What factors do we inherit that increase our risk of obesity?
  • What you can do to combat the influence of your genes to get and stay healthy.


About Dr. Fung, Author of The Obesity Code and The Diabetes Code

Dr. Jason Fung is a medical doctor, nephrologist by trade, who specializes in kidney disease, type 2 diabetes, and obesity. He acknowledged that traditional medicine wastes time and resources attempting to treat symptoms of disease, rather than the cause of disease.  

You can purchase The Obesity Code book HERE. Most information in this post is direct from this book. 


Overview of the Book

Here is an outline of the book. Today I’m covering Chapter 2: Inheriting Obesity, in Part 1 of the book. 

  • Part 1: “The Epidemic,” explores the timeline of the obesity epidemic and the contribution of the patient’s family history. It highlights the underlying causes of obesity. 
  • Part 2: “The Calorie Deception,” reviews the current caloric theory in depth and highlights the shortcomings of the current understanding of obesity. 
  • Part 3: “A New Model of Obesity,” describes how hormones are involved in the development of obesity. These chapters explain the central role of insulin in regulating body weight and describe the vitally important role of insulin resistance. 
  • Part 4: “The Social Phenomenon of Obesity,” dives into childhood obesity and why obesity is associated with poverty. 
  • Part 5: “What’s Wrong with Our Diet?,” explores the role of fat, protein, and carbohydrates, the three macronutrients, in weight gain. In addition, it examines one of the main culprits in weight gain - fructose - and the effects of artificial sweeteners. 
  • Part 6: “The Solution,” provides guidelines for lasting treatment of obesity by addressing the hormonal imbalance of high blood insulin through proper nutrition, sleep, and stress management.  


Inheriting Obesity 

It is fairly obvious that obesity runs in the family. Heavy parents tend to have heavy children. Childhood obesity is associated with a 200 to 400 percent increased risk of adult obesity. But how much of this tendency to gain weight is genetic vs environmental?


Nature Vs Nurture: The Environment 

Obesity has become a big problem only since the 1970s. Our genes can’t change that fast in 50 years. Something else is going on. Genetics can explain why a child is at a higher risk of obesity if their parents are heavy, but it doesn’t explain why an entire population became obese.  

Historically, all of the blame for “inheriting” obesity has fallen on the environment that encourages eating and discourages physical activity. Dietary and lifestyle habits have changed considerably since the 1970s including:  

  • Low-fat, high carbohydrate diets
  • Eating more frequently throughout the day
  • Eating out more often
  • Increased fast food restaurant options
  • More time spent in cars/traveling
  • Increased time spent playing video games, watching TV, and using the computer
  • Increased sugar intake
  • Increased use of high-fructose corn syrup
  • Increased portion sizes  

The common environmental argument is that parents tend to give poor eating and exercise habits to their children, who then go on to gain weight. It makes complete sense, so not much thought has gone into whether or not there is a genetic link to inheriting obesity. 

Kind of like not much thought went into determining if the “eat less, exercise” more recommendations were really working because, based on the “calories in, calories out” model of thinking, it made complete sense (read more about that HERE). 

But the evidence is proving our commonly held, long-standing beliefs about obesity are incomplete, and sometimes just plain wrong.  


Nature Vs Nurture: The Genes 

The classic way for trying to determine the genetic impact (vs lifestyle) on a disease is by comparing adoptees to their biological and adoptive parents. This way the gene aspect is controlled for, and we can focus solely on the environmental impact.  

Dr. Stunkard, a Denmark researcher, studied 540 Danish adult adoptees. He compared their weight to their biological and adoptive parents. His theory was that if environment was more important, the adopted adults weight would resemble the adoptive parents. If genetics were more important, they would resemble their biological parents.  

No relationship was found between the weight of the adoptive parents and the adoptees! The environment provided by the adoptive parents, whether they were healthy or not, made no difference.  

This finding was very surprising as standard calorie-based theories blame environmental factors (like junk food and inactivity), and human choice for obesity. But this was not found to be the case at all.  

Comparing adoptees to biological parents showed a strong, consistent correlation between their weights. Even though the biological parents had little to nothing to do with the environment in which the child was raised (the foods, activities, attitudes, and education), the tendency to become obese still followed them.  

To sum it up, you can take the kid out of the environment but you can’t take the genes out of the kid.  

Another way to study genetic vs environmental impact is to study twins who grow up in difference environments. Dr. Stunkard did another study with both fraternal and biological twins and found that 70 percent of the tendency to gain weight is determined by the genes you inherit from your parents.  

Other studies also indicate weight is under strong genetic influence, with heritability estimates from family, adoption, and twin studies averaging more than 50%.3  


Debunking the “Thrifty-gene” Hypothesis 

Dr. Fung is quick to discredit the thrifty-gene hypothesis. This is the theory that all humans are genetically predispositioned to overeat and store extra weight in case of a famine.  

The thrifty-gene hypothesis assumes chronic food shortages prevented obesity but this is just incorrect. Many traditional societies had plenty of food year-round but obesity did not occur until the Westernization of their traditional diet. Even in America, widespread famine has been uncommon since the Great Depression (1929-1939) and the growth of obesity only started in the 1970s.  

There is no survival advantage to carrying a high percentage of body fat. Being lean meant that one was more agile and able to hunt, gather, and survive. For example, a male marathon runner with 5-11% body fat still has enough energy to survive about a month without food.  

Dr. Fung makes an interesting observation between being fat and being obese. Some animals like bears, whales, and elephants are genetically programmed to be fat. For them, being fat is healthy. For humans, excess weight usually is accompanied by illness like joint pain, high blood pressure, high cholesterol, high blood sugars. It is not a coincidence that excess weight usually precedes osteoarthritis, cardiovascular disease, and type 2 diabetes.  

While this was a compelling argument, I still wanted a little more specific research indicating what WAS the genetic link with obesity. 


Additional Research: Genetics and Obesity 

Tall parents tend to have tall children, a “pear-shaped” mom is more likely to have a “pear-shaped” daughter. There is a reason why our body types tend to mirror our parents. Here are two reasons why.  

1. Body fat distribution. If your parents tend to gain weight around the midsection (or hips, thighs, or breasts), so will you.3 2. Lower satiety (feeling of fullness), leading to higher food intake.3, 4  

Other research suggests our increasingly unhealthy environment might be amplifying the genetic risk for obesity, and that changing our environment may help reduce the impact of our genes.2  

The Llewellyn et al study also states a causal association of obesity with type 2 diabetes, heart disease, specific cancers, and other conditions. This helps us determine which outcomes and diseases could be preventable through weight loss interventions.2 This is exactly why I started Reshape!


Bottom Line 

The tendency to develop obesity is up to 50% hereditary. However, both your environment and genes combine to determine risk for obesity. Individuals who are less responsive to internal cues that they are full may be more likely to eat excess unhealthy food in today’s environment where that is so easy to come by, especially in schools.  

This knowledge is good news! It means that one way to treat obesity is by helping people adopt nutritional habits that focus on eating more nutritious, filling foods and less foods that tend to lead to overeating.  

Foods that contain protein and fat will help you feel fuller for longer, and they are hard to overeat. Foods high in sugar and refined grains like chips, pop, cereal, and candy don’t fill us up. These foods actually trigger a hormonal response in our brain that leave us craving more. This makes it very easy to consume a lot of calories with little nutritional value, leading to excess weight, a sluggish mind, and fluctuating energy levels throughout the day.  



1. Chapter 2. (2016). In J. Fung, The Obesity Code: Unlocking the Secrets of Weight Loss. Vancouver: Greystone Books. *This chapter is the reference for all material in this post except that noted by another reference.  

2. Goodarzi, M. O. (2018). Genetics of obesity: what genetic association studies have taught us about the biology of obesity and its complications. The Lancet Diabetes & Endocrinology, 6(3), 223-236.  

3. Llewellyn, C. H., Trzaskowski, M., van Jaarsveld, C. H., Plomin, R., & Wardle, J. (2014). Satiety mechanisms in genetic risk of obesity. JAMA pediatrics, 168(4), 338-344.  

4. O'rahilly, S., & Farooqi, I. S. (2009). Human obesity as a heritable disorder of the central control of energy balance. International Journal of Obesity, 32(S7), S55. 

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