Have scientists discovered what’s really making us fat?

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1. Have we got it wrong about fat and sugar?

Nearly two thirds of adults in the UK are obese or overweight. Although over half of us have tried to lose weight in the last two years, many people find the weight creeps back on again. Why is it so hard to stop piling on the pounds?

Eating lots of either fat or sugar add extra calories to the diet. But the latest research suggests the real danger lies in foods that combine the two.

And the bad news is these are the very foods that we find most tempting.

2. Which doughnut would you choose?

Unlikely as it may seem, the first clue in solving the puzzle to what's making us fatter and unhealthier might lie in this tempting selection of doughnuts.

Enticing icing

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Enticing icing

Too sweet!

This doughnut is extra sugary because of the icing. It is less popular than the glazed doughnut, which has an almost 50:50 ratio of fat to sugar.

Amazing glazing

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Amazing glazing

Just right!

This doughnut hits the ultimate sweet spot of combining fat and sugar – pretty much a 50:50 ratio. It tends to be a bestseller worldwide.

Cream dream

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Cream dream

Too creamy!

The cream makes this doughnut feel like a higher fat experience. It is less popular than the glazed doughnut, which has an almost 50:50 ratio of fat to sugar.

3. The dangers of combining fat and sugar

Watch the video below to see the results of a groundbreaking experiment that turned rats into the rodent equivalent of couch potatoes.

(from Horizon: Sugar v Fat, BBC Two)

4. Why modern diets might be to blame

Studies on people show diets high in sugar AND high in fat lead to more weight gain than either fat or sugar alone. In other words, it seems that we are just like the rats.

So why does this happen?

Foods that are high in both fat and sugar almost never occur in nature. These foods are very energy dense, so are high in calories. They are also unbelievably pleasurable, and we learn to associate them with treating ourselves and feeling good.

Eating these foods supercharges the brain's reward system, activating the same neural circuits that are triggered by taking drugs like heroin or cocaine. These foods can overpower our body's ability to tell us to stop eating, so there's nothing to stop us heading to the fridge for a little extra something.