Wednesday July 9 2008
Food diaries were included as part of a wider weight loss intervention
“Keeping a food diary helps lose weight” is the headline in The Daily Telegraph. Scientists suggest that simply writing down everything that you eat can “double the amount of weight lost”, according to a new study following 1,700 volunteers over six months, the newspaper says.
The newspaper reports are based on the conclusions of an initial “screening” phase to see whether participants are suitable to take part in a trial aimed at investigating and comparing longer-term strategies for weight loss. The food diary was combined with several dietary and activity targets as part of a structured behavioural programme, which included regular follow-up and supervision by trained professionals. Although a food diary may be beneficial as part of a comprehensive weight loss programme, the amount of weight that might be lost from just keeping a food diary without other interventions cannot be accurately concluded from this study.
Where did the story come from?
Jack Hollis from Kaiser Permanente Northwest, Oregon, US, and colleagues from several other nutrition and research institutions across the US, carried out this research. The study was funded by the National Heart, Lung and Blood Institute. It was published in the peer-reviewed medical journal: American Journal of Preventative Medicine.
What kind of scientific study was this?
This was a case series where all participants received a non-randomised behavioural intervention aimed at losing weight to see whether they were eligible to enter the randomised part of the trial. It is the first six-month screening phase of a longer-term, randomised controlled trial – the Weight Loss Maintenance Trial – which has been carried out in four centres in the US. It was designed to investigate and compare alternative strategies for long-term weight management over a prolonged 30-month period.
During this first phase, 1,685 participants were invited for screening. They were all at risk for cardiovascular disease, were aged 25 or older, were overweight (body mass index [BMI] 25–45), taking medication for blood pressure or high cholesterol, and were willing to follow a healthy eating pattern. They had to agree to keep a five-day food diary and try to lose 4kg of weight. The study did not include those with medicated or poorly controlled diabetes, those who had a cardiovascular event in the past 12 months, kidney disease, psychiatric hospitalisation in the past two years, problems with alcohol or binge eating, those who had had previous weight loss surgery, those who were pregnant or breast feeding, or those with cancer in the past two years or any other contraindications to weight loss.
The weight loss intervention involved 20, weekly, 90-minute to two-hour long group sessions led by nutrition or behavioural counsellors. The intervention used a self-management and motivational approach aimed at calorie reduction and increased physical activity. Guidance for participants included consuming 500 fewer calories every day, exercising for 180 minutes each week, keeping a daily food, drink and exercise diary, aiming to find five extra opportunities every day to move more, eating 9-12 servings of fruit and vegetables and two to three daily servings of low-fat dairy food, eating less salt, and drinking no more than one unit of alcohol for women or two units for men per day. They were encouraged to be active study participants, to attend all intervention sessions and clinic visits, and aim for 4kg of weight loss. Those who achieved the target weight loss would be eligible for the randomised part of the trial.
At the end of this screening phase, the researchers measured how much weight people lost, and used statistical methods to look at what demographic, socioeconomic and behavioural factors were associated with greater weight loss. They also looked at the interaction of these factors.
What were the results of the study?
The average age of participants in the screening phase of the study was 55. Overall, 67% were women and 44% were African American. All were overweight and 79% were obese (with a BMI over 30); 87% were taking blood pressure medication and 38% were taking cholesterol medication. On average, the participants attended 14 of 20 possible sessions, and 92% of the sample had their final weight assessed. There was variability across sexes and ethnicities on the targets that were reached, e.g. the number of fruits and vegetables consumed, or the amount of activity taken. In general, weight declined during the study period by an average of 5.8kg, with 69% achieving the target weight loss of 4kg.
When researchers looked at what factors affected weight loss across the study, they found that greater weight loss was associated with keeping more diet records, attending more group sessions, taking more moderate intensity exercise and having greater weight at entry. The researchers found that for the same amount of exercise, men lost more weight than women, regardless of race. They also found that keeping a food diary increased weight loss more among non-African Americans than African Americans, regardless of gender.
What interpretations did the researchers draw from these results?
The researchers conclude that the behavioural intervention of the Weight Loss Maintenance Trial produced substantial weight loss over 20 weeks in an overweight population with risk factors for cardiovascular disease.
What does the NHS Knowledge Service make of this study?
The initial phase of the carefully designed Weight Loss Maintenance Trial was well conducted. However, its results have been misinterpreted by some news reports.
- This was not a randomised trial and was only the initial observational “screening’” phase to allow entry of participants into a randomised controlled trial aimed at investigating and comparing longer-term strategies for maintaining weight loss.
- The food diary was not an isolated intervention but was combined with several dietary and activity targets as part of a structured behavioural programme, including regular follow-up and supervision by trained professionals.
- The details of the self-reported measures of food diaries kept, activity taken and food consumed cannot be reported, as they are not described in detail in this research. However, it is likely that there will be some reporting bias in the results.
- The study period was relatively short and whether weight would be regained once the food diary and other interventions were stopped has not been reported in this publication.
- The participants in this study also had to fulfil very specific entry criteria and cannot be assumed to be representative of the general population. The study also included a high proportion of African Americans. Results may not be representative of other groups with a different ethnic makeup.
Although a food diary may be beneficial as part of a wider intervention aimed at weight loss, no quantification of the amount of weight that may be lost from keeping a food diary alone can be accurately concluded from this study, as it has not been investigated as an isolated intervention.