How to diet

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."

How to lose weight the healthy way

We put on weight when the amount of calories we eat exceeds the amount of calories we burn through normal everyday activities and exercise. Most adults need to eat less and get more active.

The only way to lose weight healthily and keep it off is to make permanent changes to the way you eat and exercise. A few small alterations, such as eating less and choosing drinks that are lower in fat, sugar and alcohol, can help you lose weight. There are also plenty of ways to make physical activity part of your life.

If you're overweight, aim to lose about 5-10% of your starting weight by losing 0.5-1kg (1-2lb) a week. You should be able to lose this amount if you eat about 500 to 600 fewer calories than you need a day. An average man needs about 2,500 calories a day and an average woman about 2,000 calories to stay the same weight.

Find out whether it's safe to lose weight fast.

Six ways to kickstart your healthy weight loss plan

Here are six simple things you can do to eat healthily and help you lose weight. You'll find lots more tips and information in our lose weight section.

  • To reduce the amount of fat you eat, you could trim the fat off meat, drink skimmed or semi-skimmed milk instead of full fat, choose a reduced- or low-fat spread, and replace cream with low-fat yoghurt. Find out about some more healthy food swaps.
  • Eat wholegrain foods, such as wholemeal bread, brown rice and pasta. They're digested more slowly than the white varieties, so will help you feel full for longer.
  • Don't skip breakfast. A healthy breakfast will give you the energy you need to start the day, and there's some evidence that people who eat breakfast regularly are less likely to be overweight.
  • Aim to eat at least five portions of a variety of fruit and vegetables a day. Learn more in Why 5 A DAY?
  • If you feel like a snack, try having a drink first, such as a glass of water or cup of tea. Often we think we're hungry when really we're thirsty.
  • Swap drinks high in calories for lower calorie alternatives – that means drinks that are lower in fat, sugars and alcohol. Swap a sugary fizzy drink for sparkling water with a slice of lemon. Don't forget that alcohol is high in calories, so cutting down on alcohol can help you control your weight.

Exercise and weight loss

Regular physical activity will not only help you lose weight, but could also reduce your risk of developing a serious illness. 

The amount of physical activity that is recommended depends on your age. Adults aged 19 to 64 who are new to activity should aim to build up to 150 minutes of moderate-intensity aerobic activity a week.

Learn more about physical activity guidelines for adults.

Page last reviewed: 09/12/2015

Next review due: 09/12/2017


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The 9 comments posted are personal views. Any information they give has not been checked and may not be accurate.

anniejig said on 16 October 2015

I was disappointed to read this terribly misinformed article.

Suggesting that cutting out meat, wheat or dairy is dangerous is misleading and potentially harmful in itself (depending on an individual's capacity to process these foods).

People look to the NHS for reliable information to keep themselves healthy and this article is less than satisfactory.

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Gilliantwo said on 15 August 2015

Disheartening to see the NHS giving potentially useful information mixed up with poor, misleading and downright false information.

For example. 2,000 calories a day for the average woman to stay the same weight. Fine if you plan to stay overweight and get heavier. Research has already proven that if most women ate 2,000 calories a day consistently they would put weight on.

Even your own BMI calculator tells me (after I realised I had to apply some brain power to deciphering the woolly language) I should not be eating more than 1500 calories a day to stay at my current weight which is overweight by a good stone.

I don't have room here to go through this with my thoughts on it all but I do think the public deserve better.

A massively new approach is desparatly needed in the midst of the obesity epidemic and serious new research needs to be done into a) what it is the very few are doing that does lead to weight loss and keeping it off and b) why are the very many who try to lose weight have failed.

I devised my own diet by spending about 4 weeks sifting through information from many sources to try and find the useful stuff - loss of 2lbs a week, 2 stone gone already. Feeling great.

I suspect the big food business and the diet industry is really in control here - to the benefit of shareholders only. When will the government get the guts to deal with them, offer 100% properly researched advice through the NHS and stop demonising overweight/obese people.

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cbt4me said on 20 May 2014

Most diet books or plans miss the fundamental notion that it is how we think that makes us fat. Addictions and cravings need to be overcome or controlled before long term and permanent weight or fat loss can be achieved.

Would you try and overcome alcoholism by consuming drinks with less alcohol in them or by saying you cannot drink 5 days a week but on the other 2 days it is fine? No.

A new approach is needed.

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Aingealag said on 27 February 2014

Hang on, let me get this straight; we humans have evolved without eating wheat and most other grains, but cutting it out is dangerous?! What can wheat provide my body with that I can't get elsewhere? And what about the ever-mounting amount of research showing that wheat/gluten have negative effects on our bodies? Read the book Wheat Belly.

I am part of a very large group of people that have cut wheat/gluten out of their diet and have felt amazing ever since. I had a standard check-up recently and my blood test results were near perfect for the first time in my life.

This article comes across as outdated and narrow-minded.

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paulgato said on 21 May 2013

"...there’s no evidence that toxins build up in our bodies. If they did, we would feel very ill."

Errm, not really true. When toxins are present in the bloodstream we feel ill, but when locked away in fat deposits for example, we don't feel ill. De-toxing is, broadly speaking, a two-stage process whereby toxins are a) released from where they are locked away into the bloodstream (where they can indeed make us feel temporarily nauseous or headachy) and then b) eliminated from the body (via liver, kidneys, bowel, skin, etc.)

“Detox diets do not work,” says Arens. “They are, in effect, a form of modified fasting.”

Well, yes, they do work, for de-toxing, but they don't work well for losing weight. Yes, they are usually a modified form of fasting.

(Traditional fasting where no food is eaten tend to be uncomfortable, as toxins are not eliminated via the bowel and are re-circulated in the bloodstream where they can cause nausea and persistant headache. Modern de-tox programmes generally work better and are more comfortable, as the bowels are kept moving.)

People who fast or 'de-tox' in order to lose weight invariably put on even more weight after the fasting period. De-toxing can be a great thing to do, but it is not an appropriate tool for weight loss.

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User684192 said on 08 June 2012

This page alone offers so much confusing information and continues the myths of weight loss for the average person. Many of the so called fad diets do not try to calculate and calorific value because it really is very difficult to do. There really isn’t a one shop blue print for weight loss there has to be some individuality and it has to be about moderation, life style and choice.

Any diet that offers to count the calorific value of food for you and make it easier to measure what it is that you are eating has to be a good thing. It is true that any diet that reduces fats and carbs will lead to calorie reduction and weight loss. But from my research successful weight watchers need to develop a life style in balance with their diets to achieve longer lasting results.

It has been documented several times that high protein diets can be harmful but the story doesn’t end there. I have achieved success and so have many of my clients with an increase in protein, a balance of fats and carbohydrates from complex and fibrous sources. So the answers are not about black and white this or that but more about readdressing the balance and moderations.

The facts that I see are that as a species we have developed scientifically faster in food production that physiologically as humans. This means that high processed foods, high sugar foods are more than our bodies can cope with and when eaten result in weight gain.

I advocate cutting out the obvious sugars in alcohol, fizzy drinks and sweets. Consume moderate amounts of carbohydrate in the form of pulses, beans and other complex whole grain carbs. Increase our protein intake from lean sources and combine whole grains and beans to form healthy and cheap sources of amino acids. Fats are not the enemy and are needed in moderation for cell integrity and absorption of some vitamins and minerals. Choose fats that are natural such as olive oils and omega oils.

Exercise has to be realistic so start walking and enjoy.

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User363614 said on 02 June 2012

So, eating a diet that our species evolved with, that largely excludes grains for instance, is a fad diet. Whereas getting a third of what we eat from starchy carbohydrates, that are mainly processed foods (have you tried eating wheat in its husk?) is healthy eating. Now I understand. I just don't believe it.

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User681112 said on 29 May 2012

@ Grumpya - it can be confusing, but there are plenty of daily calorie requirement calculators out there to find yours. You're right, I work in healthy weight loss including for the NHS and have clients who need to eat 1200cal to lose weight and some that will lose weight on 3000cals! It's entirely dependent on your height, weight, age and physical activity level. Look for calculators based on the Harris Benedict equation for an accurate measure of your own requirement. It's suprisingly simple to lose weight in a healthy way when you start ignoring the branded "diet" fads and go for good real food rather than products.

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grumpya said on 24 March 2012

Just saying eat 5 to 600 calories a day less than you nheed is no good if you don't have a calculator for how many calories you need. Women may average 2000 calories a day but there is a huge difference between a 20 stone woman's calorie needs & a 9 stone womans needs likewise with men likewise with activity levels. Big difference between a typist & a tree surgeon or lorry driver & a builder. This page needs to give a bit more info

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