What Causes Weight Gain?

There are lots of myths out there about how to best lose weight.

It can be confusing and difficult to know what information you can trust.

Let’s take a look at the current evidence;

On the one hand, it is a simple energy balance equation – if we have more energy coming in than going out – then weight will be gained. But the causes of weight gain are actually far more complex than this. Weight gain is caused by the following factors:

  • Genetic
  • Physiological
  • Environmental
  • Psychological

Until now, we have focused on lifestyle factors alone, often blaming the person who is overweight for their condition.

But now we are recognising the important role that genetics play and that obesity really is a chronic disease that needs to be managed like any other, with a wholistic approach.

How is Weight Controlled?

Proietto J. Why is treating obesity so difficult? Justification for the role of bariatric surgery. Med J Aust 2011; 195(3):144-146.
© Copyright 2011 The Medical Journal of Australia – reproduced with permission.

Our body weight is controlled by a special part of the brain, called the hypothalamus. It is like the control centre of a ship – it likes to keep everything steady – blood sugar, blood pressure, body temperature, and of course – body weight.

When we try to lose weight, the body will try to restore you to your “set point” of body weight, by increasing hunger and decreasing incidental activity. That is why so many people will put weight back on after losing it.

What determines our set point
of body weight?

Each person has a different set point, some have a lower set point and are “naturally thin” whilst others will have a higher set point of body weight and will tend to put on weight easily.

Our set point of body weight is determined by the genes that we inherit.

The Role of Genetics

Most people believe that those who carry extra weight choose to do so, but this is simply untrue. There is overwhelming evidence that weight excess is largely determined by our genes and then triggered by our environment.

Twin studies demonstrate a very strong correlation (0.74) of weight between identical twins. Even if those twins were adopted and reared in different families, their weight correlation with each other was still 0.70, even though they had never met each other!

Adoption studies also show that children reared apart tend to match their biological parents rather than their adoptive parents, showing us how important genes are in determining weight.

There is no one gene that causes obesity but there are approximately 100 genes contribute to weight gain. For any one individual, the contribution of genetics to their weight is somewhere between 40-70%.

How do genetics affect my weight?

Genetics will affect our hunger and appetite hormones, our tendency to fidget and “waste energy” and our set point of weight.

People who carry extra weight will have higher levels of the hunger hormone — ghrelin, and reduced sense of fullness even after a large meal.

What About Lifestyle?

We have also seen a dramatic increase in weight gain in the last 30-40 years. This is due in part to the vast changes in our lifestyle – more junk food, food on the go, high calorie foods readily available and reduced physical activity.

But not everybody becomes overweight in this environment – so you do need a genetic susceptibility to become obese.

“Our genes load the gun and environment pulls the trigger”

George Bray, obesity researcher

Fighting the Urge to Eat

So whilst the causes of weight gain are complex, we can’t be successful in treating weight, unless we take care of hunger and help our body to feel full.

If we don’t, then it’s like trying to outsmart one our body’s smartest systems – our primitive drive to survive.

Most people who try to lose weight just restrict their diet and feel hungry and therefore, can’t sustain it.

Hunger is the body’s physiological defence against weight loss – a survival advantage for our caveman ancestors.

Why is it so difficult to keep the weight off?

After losing weight, the research tells us that there are three important things that happen in response to weight loss:

  • Hunger hormones remain elevated
  • Fullness hormones drop and
  • Energy expenditure drops

to encourage the body to regain weight – a so called survival advantage – but a big problem if you battle with weight.

These changes persist for at least 1 yr and probably indefinitely after weight loss (Sumithran et al, 2011). The increase in hunger hormones that we see, is the reason why 95% of people who lose weight, regain it again.

Can you beat the battle with biology?

If we are to be successful in the long term, we must overcome the body’s natural tendency to protect us against weight loss.

The key to this is feeling full. If you are hungry, you will be driven to eat, no matter how good your self control is.

Try holding your breath and see what happens, your body will make sure you breathe – and it is the same with food.

But if we feel full and satisfied, then we can make the body think that it is more comfortable at a lower set point of body weight and so long term weight control becomes a realistic and achievable goal!