For years, people wanting to lose weight have been advised to follow a low-fat diet. But a big new study shows that this type of diet may not be the best bet for long-term weight loss.
What do we know already?
The standard diet recommended to people losing weight is a low-fat diet. You cut down on fat and eat plenty of fibre, fruit, vegetables and complex carbohydrates like rice and wholemeal bread or pasta.
Two other diets have attracted attention recently. One is the Mediterranean diet, where people use olive oil instead of saturated fats like butter, eat plenty of fruit and vegetables, and eat fish or chicken instead of red meat. The other is the low-carbohydrate diet, where people cut down on carbohydrates such as pasta and bread rather than on fat. This last type of diet includes more fat from meat and dairy products.
A new study compared how more than 300 overweight people did on the three diets, over a 2-year period. You need to look at the long-term picture with diets, as people often lose weight at first, then put it back on again.
What does the new study say?
In the new study, people following a low-carbohydrate diet, or a Mediterranean diet, lost more weight than those on a low-fat diet, even though they reduced the calories they ate by about the same amount.
This is how much weight people lost, on average:
- 2.9 kg on the low-fat diet
- 4.4 kg on the Mediterranean diet
- 4.7 kg on the low-carbohydrate diet
The differences between the amount of weight lost on the Mediterranean diet and the low-carbohydrate diet were small enough that they could have been down to chance.
Tell me more about the study's findings
There were plenty of other interesting findings in the study.
- People in the study lost most of their weight in the first six months. They put some back on during the next year, but their weight was stable from around 18 months to two years.
- People on the low-carbohydrate diet ate more saturated fat, but had more 'good' cholesterol in their blood compared to people on the low-fat diet.
- Most of the people in the study were men. Men lost most weight on the low-carbohydrate diet, but women lost most weight on the Mediterranean diet.
Where does the study/report come from
The study was carried out by researchers and dietitians from Ben-Gurion University, Israel. It was published in the New England Journal of Medicine, which is owned by Massachusetts Medical Society. It was funded by the Negev Nuclear Research Center (where the study was carried out), the Dr Robert C and Veronica Atkins Research Foundation, and the S Daniel Abraham International Center for Health and Nutrition.
How reliable are the findings?
The study was carried out carefully. It's one of the first good quality studies comparing different types of diet for losing weight over a long time.
The people taking part in the study all worked for the same company and ate lunch in the workplace cafeteria. The study organisers sent nutritionists to work with the cafeteria staff to make sure everyone had well-labelled options that fitted with their diet plan. The people in the study had regular meetings with nutritionists and were weighed once a month. They were also encouraged to do exercise. So they had a lot of support to make it easier for them to stick to their diets. It may be harder for people not in a workplace like this to stick so well to their chosen diet.
What does this mean for me?
If you need to lose weight, you need to find a diet that works well for you and that you can stick to over a long period. This study shows that a Mediterranean diet and a low-carbohydrate diet work at least as well as, if not better than, a traditional low-fat diet. The important thing is to stick to the diet you choose, and to take exercise. Other studies have shown that getting help and support during your diet can help you stay on track.
What should I do now?
If you are worried about your weight, a good place to start is your GP. Your GP will be able to help you work out your body mass index (BMI) to see if you are overweight. He or she may also be able to recommend local classes or support groups that can help you plan and stick to a diet.
Shai I, Schwartzfuchs D, Henkin Y, et al. Weight loss with a low-carbohydrate, Mediterranean or low-fat diet. New England Journal of Medicine. 2008; 359: 229-241.
To find out more, see our information on Obesity.
© BMJ Publishing Group Limited ("BMJ Group") 2009