A team of academics in Canada set out to assess the evidence from existing studies on 100% fruit juice consumption and body weight in children and adults.

The study was a systematic review and meta-analysis (super study) of mostly observational studies lasting months or years [1]. Observational studies are not designed to establish cause and effect since they don’t control for the many factors that affect body weight including exercise or other foods and drinks with high fat or sugars.

The team’s analysis of the data found a statistically significant relationship between drinking a serving (237ml) of 100% fruit juice and a body mass index (BMI) gain of 0.03 in children. But what does that mean in real life?

Registered Dietitian Dr Carrie Ruxton comments: “In an average child (1.3-1.4 metres tall), this 0.03 change in BMI equates to a 60g weight increase over the average study duration of 4 years. This is clearly negligible from a health perspective since 60g is the weight of a small piece of banana – which isn’t going to make anyone obese.”

In the case of adults, the researchers looked at observational studies with an average follow up of 3 years and found a statistical association between drinking more fruit juice and weight gain. Again, this is less impressive when actual weight change was calculated.

Dr Ruxton points out: “The average gain in weight was 210g for each serving of fruit juice which, again, is negligible and would not cause obesity in adults.”

It’s emphasising that the standard serving size chosen by the researchers as a cut-off for analysis – at 237ml or almost quarter of a litre – is far higher than maximum servings recommended in many European countries (100-200ml). This type of fruit juice intake may be normal in America but doesn’t bear any resemblance to average European intakes which are 137 grams a day in adults and 108 grams a day in school-aged children [2].

Dr Ruxton adds: “Different results were seen when American and European studies were considered separately. In the American studies, there were significant associations between fruit juice intake and BMI in children, as well as body weight in adults. In contrast, statistically significant associations were not found for the European studies. This suggests that the overall results for fruit juice were not reflective of the situation in Europe”.

Significantly, randomised controlled trials on fruit juice in adults found no significant impact of fruit juice on body weight over several weeks. These types of studies are higher quality than the observational studies used for the other analyses as they can control for confounding variables. In children, there were no intervention trials to compare.

In the randomised controlled trials where adults drank less than 237ml daily, there was a significant reduction in body weight compared with those drinking more than 237ml daily. This suggests that moderate fruit juice consumption may even be beneficial for body weight control.

Dr Ruxton concludes: “While this meta-analysis was useful, the real impact on body weight in adults and children was negligible and would not be expected to influence risk of obesity. Not only this, but intervention studies in adults directly contradicted the results from the observational studies, casting doubt on the findings. We need more studies in European populations as they have different intakes of 100% fruit juices to Americans”.

Reference

1. Nguyen M et al. (2024). https://pubmed.ncbi.nlm.nih.gov/38227336/

2. Walton J & Kehoe L (2024) Current perspectives and challenges in the estimation of fruit juice consumption across the lifecycle in Europe. Nutrition Research Reviews, in press. https://pubmed.ncbi.nlm.nih.gov/38356367/