Thursday November 25 2010
“Protein-rich diets containing lots of lean meats, fish and egg – as popularised by the Atkins diet – are the best at keeping weight off,” reported The Daily Telegraph. It said that people who stick to this approach can simply eat until they feel full and not put on weight.
This study compared five diets to maintain weight loss in people who had recently lost at least 8% of their weight through dieting. None of the diets were calorie-controlled, but had different amounts of protein and varied in their glycemic index (GI – a measure of the effect that carbohydrates have on blood sugar levels and how quickly food is digested).
There was less weight gain with high-protein diets than low-protein diets. People on a low-GI diet regained less weight than those on a high-GI diet. The only diet linked with significant weight regain was a low-protein, high-GI diet.
This large, well-conducted study appears to support the idea that high-protein, low-GI diets are better at maintaining weight loss than other types of diet. However, an Atkins diet was not tested, as the high-protein diet used in this study only included protein as 25% of the total energy consumed, compared with 50% in an Atkins diet. Also, the difference in protein levels between this and a low-protein diet was only modest (13%).
Finally, these diets were not compared to a conventional calorie-controlled diet for weight loss maintenance. The study does not support extreme diets that replace most carbohydrates with protein.
Where did the story come from?
The study was carried out by researchers from research centres in several European countries, including Denmark, the Netherlands, UK, Greece, Germany and Spain. It was funded by grants from and contributions from the European Commission and by several food companies. The study was published in the (peer-reviewed) New England Journal of Medicine.
The Daily Mail's claim that calorie counting is ‘off the menu’ was misleading since the study did not compare calorie-counting diets with those which are not calorie-controlled. The rest of the paper’s report was accurate. The Daily Telegraph's claim that ‘protein-rich’ diets are the best way to keep weight off is perhaps exaggerated since the high protein diet used in the study contained only 25% protein.
What kind of research was this?
This was a large randomised trial of over 1,200 adults, in which researchers compared the ability of five different diets aimed at preventing weight gain.
The researchers say that there is still uncertainty regarding the importance of the composition of diet for the prevention and management of obesity. There is increasing interest in diets high in protein or low in GI, but so far, scientists have been uncertain about their effectiveness for maintaining weight loss compared with other types of diets.
In this study, the researchers wanted to test how successful diets were at preventing weight gain in people who had recently lost weight.
Trials in which participants are randomly assigned to different interventions are more reliable than other types of studies (such as cohort studies) for answering questions about effectiveness. This is because randomisation trials help eliminate bias and confounding factors (where things such as sex and education, may influence results).
What did the research involve?
The researchers enrolled 773 overweight adults from eight European countries (Denmark, the Netherlands, the UK, Greece (Crete), Germany, Spain, Bulgaria and the Czech Republic) who had lost at least 8% of their initial body weight with a low-calorie diet over eight weeks previously all using the same diet. The participants were randomly assigned to one of five diets aimed at preventing weight gain for a 26-week period. Participants were allowed to eat as much food they liked from their assigned diet. All five diets were designed to have moderate fat content (25-30% of total energy).
The five different diets were as follows:
- a low-protein (13% of total energy) and low GI diet
- a low protein and high GI diet
- a high protein (25% of total energy) and low GI diet
- a high protein and high GI diet
- a control diet that followed dietary guidelines and had moderate protein content
The difference in total energy from protein between high and low protein diets was 12% and the difference in GI between low- and high-GI diets was 15 units.
Participants were on average 41 years old and were all parents. The participants’ families, although not part of the trial, were assigned to the same diets. Families were given recipes and cooking, behavioural and nutritional advice. In some countries, families were also given free food from a shop that catered for their diets, while others only received advice.
The participants’ adherence to their diets was monitored using urine analysis. Urine samples were taken at various times through the trial. The participants also completed food diaries and the glycemic index and nutrient content of the food that they recorded was assessed in a standardised way using glucose as a reference point for high GI index.
Standard statistical methods were used to assess how the different diets affected weight, in particular, which diets worked best for continued weightloss. They used what is called an ‘intention-to-treat’ analysis, which means that all participants who started the trial were included in the analysis, regardless of whether they finished the trial or not. This method helps eliminate the bias that can occur when many people drop out of a trial.
What were the basic results?
The average initial weight loss with the low calorie diet used in the first phase of the study was 11kg. Out of the 938 people who entered this first phase, 773 completed it and were assigned to one of the five diets. A total of 548 people (71%) completed the 26-week diet trial period. Fewer people in the high-protein, low GI groups dropped out than in the low-protein, high-GI-group (26.4% and 25.6% respectively, compared to 37.4%).
In an analysis of the participants who completed the study, only those who were on the low-protein, high-GI diet were associated with significant weight regain (1.67kg, 95% confidence interval [CI] 0.48 to 2.87).
In the intention-to-treat analysis (all people who started the study):
- weight regain was 0.93 kg less (95% CI 0.31 to 1.55) in groups assigned to a high-protein diet than in those on a low-protein diet
- weight regain was 0.95 kg less (95% CI 0.33 to 1.57) in those on a low-GI diet than in those on a high-GI diet
How did the researchers interpret the results?
The researchers say that a ‘modest increase in protein content and a modest reduction in the glycemic index’ led to more people completing their diets and maintaining weight loss. The combination also appears to be ideal for preventing people regaining weight after a calorie-controlled diet.
While many overweight people can reduce their weight through diet, maintaining weight loss in the longer term is more difficult. This large, well-designed study found that a non-calorie-controlled diet moderately high in protein and with a slightly reduced GI index appeared to be more acceptable to people (more finished this diet than on other). The diet also helped maintain weight loss when compared with diets lower in protein and higher in GI.
This was a large well-conducted study that found that diets higher in protein and low on the GI scale worked better for maintaining weight loss than lower protein, high-GI diets. As a randomised study, the results are likely to be reliable and worth bearing in mind for individuals interested in keeping to a healthy weight. However, its findings do not support diets that include very high protein levels, or specific programmes such as the Atkins diet.
For a healthy diet, the current advice is to eat plenty of whole grains, fruit and vegetables, many of which are low on the GI scale. Protein is an important part of our diet, although requirements for protein (from fish, lean meat and poultry, eggs and small amount of dairy) vary depending on age and circumstances.