How genes and calories affect our weight


  • Living
  • Sunday, 27 Dec 2015

Fat people find it more difficult to eat less, compared to skinny people, because of their biology, according to Dr Yeo. Photo: Reuters

The prevailing opinion out there, no matter how educated you are, is that fat people are fat because it is their fault,” says University of Cambridge, in Britain, Metabolic Research Laboratories Genomics and Transcriptomics director Dr Giles Yeo.

However, that opinion is inaccurate.

“For fat people, it is always going to be more difficult to eat less than skinny people.

“The reason that it is difficult is because of your biology, not your willpower,” he explains.

It’s my genes!

Aside from the way our body has evolved to deal with food, our weight – or to be more specific, our fat mass – is also affected by our genes. Like height, our weight has a genetic component that is highly influenced by the environment we live in.

“The inheritance of fat mass – how much and where you put it – is actually equivalent, or greater, probably, to that of height,” says Dr Yeo, whose research revolves around the brain’s control of food intake and body weight.

He explains: “Where you put it – your body shape – tends to be determined by genes within your fat.

“How much fat you have, independent of where you put it, involves genes within the brain and involves food.

“That’s what all the genetic studies have shown.

“So, the genetic risk factors for how big you are lie in the genes within your brain and within your fat.”

The genes within our fat determine how easily our pre-fat cells (pre-adipocytes) change into fat cells and how big these fat cells will grow under the influence of our diet.

They also determine which part of the body is most predisposed to store fat, which is why body shapes like having a big bum, a big tummy or a big chest, run in families.

Our body takes more energy to digest a steak compared to minced beef in a lasagna as the mincing process removes one step in the digestive process. Photo: Filepic
Our body takes more energy to digest a steak compared to minced beef in a lasagna as the mincing process removes one step in the digestive process. Photo: Filepic

As for the genes within our brain, Dr Yeo says that these genes, on average, affect how hungry we feel.

The theory is that people who tend to put on weight at the drop of a hat, have genes that make their brain more resistant to the circulating hormones that signal how much fat the body has and how many calories they last ate.

“Your brain is slightly resistant to them, so it thinks that you have slightly less fat and have eaten slightly less calories in the last meal than what the hormones are trying to tell the brain it has,” he explains.

“Remember, when your brain integrates how much fat you have and how much food you have eaten, it then influences what you feel like the next time you come across food.

“So, because your brain is set to think that you have less fat and eaten less than you actually have, you are set to eat a little bit more to try to make this up,” he says.

He adds, however, that these are small effects. “For example, you have 15kg of fat, but your brain thinks it’s 14.9kg, or you’ve eaten 1,000 calories, but the brain thinks it’s 990.”

There are currently around 200 genes within the brain identified as playing a role in determining how much fat we have.

However, Dr Yeo notes that, again, the effect of each individual gene is actually very tiny.

“For example, one of the genes that I am studying – if you have two copies of the risk version of the gene, and compare yourself to someone with two copies of the non-risk version of the gene, you are, on average, likely to be three kilos heavier.

“So, we are not talking huge amounts of weight, we are talking a few kilos here and there.”

Therefore, if we are overweight, can we just give up on trying to lose weight and blame our genes?

Dr Yeo uses a poker analogy to answer.

“Here’s the thing, your gene hand in life is like a hand in poker; you can have a bad hand, you can have a good hand,

“You can win with a bad hand – it’s more difficult, but you can win – and you can lose with a good hand, depending on how you play the hand.”

More calories available

Obesity is really a contemporary problem that has largely exploded over the last few decades, says Dr Yeo.

And unlike our genes, which were shaped over millennia of evolution, one of the factors in this sudden expansion of our waistlines is the relatively recent evolution of more easily-available calories to most communities around the world.

Dr Yeo explains that the way calories are packed into foods have a large effect on how many calories are actually available to the body at the end of the day.

Taking the example of sugar, he says: “If you have 100 calories of sugar and just ate that, you would get 100 calories out of the sugar, because sugar is the most basic food source.”

This means that the calories from sugar can be used directly by the body with hardly any digestive process taking place.

However, giving the example of celery, he explains that due to the digestive process needed to break down this vegetable – which contains complex sugars, fibre and protein, among others – the body will never get the total amount of calories it contains.

For 100 calories of celery, the body would need to expend a certain amount of energy just to digest it, meaning that the net amount of calories available after it has been digested would be less than 100.

But, he adds that the way we cook the celery also has an effect on the availability of its calories to the body.

“Say you put the celery in a stew. This very same celery, you boil it for three hours.

“You’ll get more calories out of it because part of the digestion process has happened outside the body in a pot.”

Comparing the examples of a ready-made lasagna meal where the beef has been completely minced and boiled, a hamburger made of ground-up meat, and a steak, he says that gram for gram, with the same amount of calories and fats, each type of food would provide different amounts of calories to the body due to the way the beef has been presented.

“You’re going to get a lot more calories out of the beef that has been completely minced and boiled, compared to the beef that has been ground-up and compared to the steak.”

He adds: “The problem we have today is that the food we have, for better or for worse, is more processed.

“On top of that, there is the refinement of calories. For example, highly-refined sugars and highly-treated flours.”

This refinement, he explains, is a process that removes one step – thus, saving the body the need to use up energy for that step – from the digestive process within the body.

“So, throw all that together and you could argue that actually being obese in the current environment is the natural thing.

“That we are responding like we were designed to respond,” he says.


Tan Shiow Chin was a 2015 Khazanah-Wolfson Press Fellow at Wolfson College, University of Cambridge. This article is part of a series from her fellowship project on the subconscious cues that influence us to eat more and unhealthily. Her next article will be on the influence of advertisements on our food choices.

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