The average weight has soared over the past 20 years and now, almost a quarter of the adult population is clinically obese. So what makes one person thin and another morbidly obese? As Dr Gabriel Weston discovers in the documentary The Truth About Sugar, weight loss or gain has less to do with diet, exercise and willpower, and far more to do with our genes and hormones.
Siobhan Hegarty

9 Jul 2014 - 11:55 AM  UPDATED 25 Jul 2014 - 10:45 AM

1. Fatty food is a primitive urge

Why do we crave foods that are high in sugar and fat? Our bodies evolved from a prehistoric world where calories were scarce and fat meant survival. Nowadays, calorie-rich foods are plentiful, so it’s easy to find a quick, unhealthy fix. This ease of access is producing dire results. Estimates suggest that some of us are eating 200 or more calories than we need every day.

2. Our hormones make us feel hungry or full

Hormones are a group of proteins that course through our bodies every day. They tell our bodies when to fight or flee, how to repair itself and even when to die. Researchers have recently found two hormones, known as Ghrelin and PYY, that work together to control our appetite and weight. They help us feel hungry and full, and prove how the gut can talk to the brain.

3. “Fat” and “thin” genes can be switched on and off

Genes play a crucial role in determining our height and weight, but it’s not enough to just have a gene, it needs to be activated. Environmental factors, like stress and isolation, can have this affect – altering our metabolism and switching on “fat” or “thin” genes. These tiny switches will influence when and how much we eat, and how our bodies use that food.

4. Obese people aren’t necessarily hungrier

An obese person’s appetite isn’t as large as you’d think. Science shows their hunger hormone never gets switched on, but stays at the same level all day and only rises when deprived of food. Instead of pangs of hunger, obese people experience a constant nagging sensation throughout the day.

5. And many never feel “full”

When most of us eat, we wind up satiated and only consume more when hunger returns. Obese people experience things differently. Their fullness hormone will only rise a small amount after they’ve eaten, before it drops again. Many obese people never feel full, which is why they will often eat too much.

6. Surgery isn’t just a “quick fix”

Gastric bypass is a controversial operation traditionally touted as a “quick fix” for solving obesity. The operation reduces the size of the patient’s stomach, so they can no longer eat as much. The results, however, aren’t just physical. Gastric bypass will often affect the patients’ psychological relationship with food through reducing their appetite and help them experience fullness, so they lose the urge to over-eat.

7. Food produces a chemical reaction that’s out of our control

When an obese person is shown images of high-fat foods, their brain activates in the parts associated with addiction and reward. MRI scans reveal this does not occur for persons of a healthy weight. Interestingly, brain scans of obese patients who have undergone gastric bypass surgery are substantially different post-operation. Their cerebral activation is reduced to the point of mirroring a “normal” response.

8. Willpower doesn't equate to weight loss

We can’t always control our body’s “set point”. Proportions are often pre-determined, so no matter what we eat – and how often – sometimes it’s impossible to shed kilos or bulk up as much as we want. That said, diet, portion size and exercise are still essential ingredients in living a healthy lifestyle.


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