How to diet this Christmas

Low carb, the 5:2 diet, detox, cabbage soup ... there is no shortage of novelty diet programmes promising to help you lose weight fast.

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The big question is, do they work? Most do lead to fast – sometimes dramatic – weight loss, but only for the pounds to creep back on again at the end of the diet.
More worryingly, many fad diets are based on dodgy science or no research at all, prescribing eating practices that are unhealthy and can make you ill.
In 2011, the British Dietetic Association warned against following popular diets such as the Dukan diet, which it said was complicated, not based on scientific evidence and reportedly did not lead to long-term weight loss.
Below are some of the problems with fad diets, plus advice on healthy eating and how to lose weight healthily.

Five reasons to avoid fad diets

Many weight loss diets promise to help you lose weight quickly. Often these diets only focus on short-term results, so you eventually end up putting the weight back on.
Here are five reasons why following the latest novelty diet may not be a good way to lose weight.

1. Some diets can make you ill

Many diets, especially crash diets, are geared to dramatically reducing the number of calories you consume. "Crash diets make you feel very unwell and unable to function properly," says dietitian Ursula Arens. "Because they are nutritionally unbalanced, crash diets can lead to long-term poor health."
Find out how to start losing weight.

2. Excluding foods is dangerous

Some diets recommend cutting out certain foods, such as meat, fish, wheat or dairy products. Cutting out certain food groups altogether could prevent you getting the important nutrients and vitamins your body needs to function properly.
You can lose weight without cutting out foods from your diet. The eatwell plate shows the different foods we should be eating.

3. Low-carb diets can be high in fat

Some diets, such as the Atkins diet, are very low in carbohydrates (for example, pasta, bread and rice), which are an important source of energy. While you may lose weight on these types of diets, they're often high in protein and fat, which can make you ill. Low-carbohydrate diets can also cause side effects such as bad breath, headaches and constipation.
"It has been suggested that the high protein content of these diets 'dampens' the appetite and feelings of hunger," says Arens. Many low-carbohydrate diets allow you to eat foods high in saturated fat, such as butter, cheese and meat. Too much saturated fat can raise your cholesterol and increase your risk of heart disease and stroke.

4. Detox diets don't work

Detox diets are based on the idea that toxins build up in the body and can be removed by eating, or not eating, certain things. However, there's no evidence that toxins build up in our bodies. If they did, we would feel very ill.
Detox diets may lead to weight loss because they involve restricting calories, cutting out certain foods altogether, such as wheat or dairy, and eating a very limited range of foods. "Detox diets do not work," says Arens. "They are, in effect, a form of modified fasting."

5. Cabbage soup, blood group, the 5:2 diet and other fad diets are often far-fetched

Some fad diets are based on eating a single food or meal, such as cabbage soup or raw foods. Others make far-fetched claims, such as encouraging people to cut out certain foods from their diet based on their blood type.
Intermittent fasting, which includes the increasingly popular 5:2 diet, is a pattern of eating where you eat normally five days a week and fast on the other two days. Fans of the 5:2 diet say it can help you live longer and protect you against disease.
Often there is little or no evidence to back up these claims, and it can be difficult to keep to in the long term. "If followed over long periods, these diets can be very unbalanced and bad for your health," says Arens. "You may lose weight in the short term, but it's much better to lose weight gradually and to be healthy."