Do 'diet foods' make you fatter?

The benefits of low-fat processed foods have been questioned, as many replace the fat with added sugar or sweeteners. Not all calories are thought of as the same any more, with experts identifying that fat and protein have advantages over refined carbohydrates in making you feel satiated and full for longer.

The 'low-fat' trap

Studies show that we eat more when something is described as ‘low-fat’. In one study people ate as many as 28 percent more low-fat sugar-coated chocolates than normal ones. It also found that people underestimate the number of calories they consume when eating low-fat food.

Know that guilty feeling when you’ve eaten a lot of something high-calorie, high-sugar and/or high-fat? You’re not alone. But when you eat too much of a food labelled ‘low-fat’, studies show you feel less guilty, especially if you’re overweight already. Labelling snacks as 'low-fat' seems to mean people increase the serving size regardless of whether the snack is healthy or unhealthy.

A food labelled ‘low-fat’, in which the fat has been replaced with sugar, may not be as low in calorie density as you'd expect. Meringues, for example, are no-fat but very high in sugar. A diet high in ‘good’ fat is likely to be better for you than a low-fat diet that is high in sugar.

Can you consume sweeteners?

Whether it’s diet soda, saccharin instead of sugar in tea, a sugar-free dessert or sweet, or even a ready-meal, artificial sweeteners have been fully adopted into modern diets.

But what if the very things thought to help us eat less sugar and stay slimmer are actually making us fatter? Studies suggest that if you consume something sweet you appetite increases, whether the food or drink is artificially sweetened or not. This is because sweeteners activate the brain's 'sugar reward' pathways, giving you a 'sweet tooth' that can cause you to snack more. When you consume something naturally sweet you have an initial metabolic response to the sugar, but studies show that the initial neuro-physical response to artificial sweeteners is not the same.

Some artificial sweeteners also trigger insulin, which sends your body into fat storage mode and leads to weight gain.

Snack attack

Snacks that you perceive to be low fat or healthy are often not as good for you as they seem.

• Rice snacks: they may seem healthier than crisps, but some can be high in salt.
• Yoghurt raisins: while you would expect these to be sweet, a 25g portion can contain as much as 5g of fat, compared to the trace amounts of fat found in uncoated raisins.
• Low-fat yoghurt: they may have less fat and fewer calories, but they can contain as much as 10g more sugar than a plain natural yoghurt.

The key to a healthy diet

Focusing too heavily on the sugar, salt, fat and calories in food can be counterproductive when it comes to healthiness. Tips for a healthy diet include:

• Cook it yourself: cooking your own meals and snacks means that you can control how much salt, sugar and fat you put in.
• Don't focus on a single macro-nutrient: some snacks may be high in fat, but don’t rule them out. A handful of almonds, for example, contains around 7g fat, but you will also benefit from their high protein and fibre content.
• Avoid empty calories: while some foods have a high nutritional value, others are essentially 'empty calories', which means your body gets very little from them nutritionally. These include sugary soft drinks and confectionery.