Is Obesity a Choice?
Giles Yeo - Professor of Molecular Neuroendocrinology
Here Professor Giles Yeo gives an interesting talk on the genetics of obesity at the Royal Institution. He is a geneticist with over 20 years of dedicated research on the genetics of obesity. This lecture is easy to listen to, eye-opening, and I would recommend it to any patient or doctor interested in the treatment of obesity. Why do some people eat more than others? Prof Giles Yeo explains it all. Although I would strongly encourage you to watch the lecture yourself, I have summarised the key content below:
Calories in, calories out is a simple physical principle. You will gain weight if you have more calories in than out. However, the ‘calories in’ part of the equation is not exactly simple and influenced by complex mechanisms, which are largely influenced by genetics. Although not discussed in the lecture, CICO sounds like a good way to lose weight but it is very, very difficult to calculate how many calories you eat and how many calories you burn. People almost always underestimate how many calories they have consumed and overestimate how many calories they have burnt.
Genes have so much influence over your eating patterns. Even the taste of brussel sprouts (bitterness vs no bitterness) is influenced by your genes.
Some monogenic forms of obesity e.g. leptin deficiency. This is quite a rare monogenic form of obesity. Your brain seems to be sensitive to leptin deficiency (i.e. starvation) but not really sensitive to ‘too much leptin’. Injecting subcutaneous leptin did not change the weight of participants with obesity at all who did not have a genetic mutation in the leptin gene.
Labradors and food motivation/obesity genes. Labradors are one of the most trainable breeds of dogs because they are driven so powerfully by food. Guide dogs are more likely to have the obesity genotype (POMC mutation), more likely to be driven by food, more trainable, and of course, more likely to be overweight than other labradors.
1% of BMI >30 patients will have the pathological MC4R mutation that leads to uncontrollable obesity. This is also not a binary effect. The ‘quality’ of the MC4 receptor determined the amount of food that study participants (children) could eat in a buffet. The relationship between MC4R mutations/variations and food seeking behaviours were not only shown in humans, but also in mice, pigs, and also, even in ‘mexican cavefish’. If a mexican cavefish also has the genes that influence food-seeking behaviours/obesity, can we really blame ‘bad habits’ in a patient suffering from obesity?
Giles Yeo then talks about studying obesity in fruit flies! Fasting flies for 24hrs and seeing their eating/exercise habits. Is obesity and eating habits really a ‘choice’ or ‘moral failure’ when fruit flies also have hard-wired tendencies with food?
Also discussed work on genome wide association studies and common obesity. Multiple genes are implicated in obesity. Number of at-risk BMI alleles correlated well with the mean BMI of those subjects.
The genetic basis for the ‘dessert tummy’. The area of the brain that is involved in hedonic (pleasurable) eating allows us to increase the caloric density of food that we eat when we’re full. This has increased our survivability in prehistoric times. For example, in the Serengeti, after we eat an antelope, we don’t have room for another one but have ‘room’ for honey and fruit, to allow us to pack in as much energy as we can to survive our next fasting period. We all have the genes of obesity. Otherwise we would not be here.
The grizzly bear before hibernation as they get fatter and fatter, will only eat the skin and the fat of the salmon and become incredibly picky - to consume only high calorie food that will help them survive a long fast.
You are a function of 1000s of food decisions that you have made in the last few months to a few years. If your genes make it slightly more difficult for you to say no in say even 5 percent of the time, over the years, you will always be at risk of becoming slightly heavier than your peers. People with obesity are fighting their biology.