Effects of total fat intake on bodyweight in children
To try to better prevent people from being overweight and obese, we need to understand what the ideal amount of total fat in our diets should be, and particularly how this is related to bodyweight and fatness. This relationship differs in children compared to adults, because children are still growing and developing.
This review looked at the effects of eating less fat on bodyweight and fatness in healthy children aged between two and 18 years, who were not aiming to lose weight. We carried out a comprehensive search for studies up to May 2017.
We found three randomised controlled trials (clinical trials where people are randomly put into one of two or more treatment groups) conducted in 1054 children in high‐income (wealthy) countries. Two studies recruited children aged between 4 and 11 years and one study recruited children aged 12 to 13 years. The studies looked at different types of interventions, including individual and group educational sessions or advice. The sessions were delivered in clinics, schools and homes by dieticians, nutritionists or teachers. The interventions used in the studies were intended to help children to eat less total fat in their diet (30% or less of their total daily energy). These interventions were compared with a usual or modified fat intake (more than 30% of their total daily energy) for between one and seven years. Some of these results showed that a lower fat intake may reduce body mass index (BMI; a measure of body fatness based on height and weight) and the blood levels of different types of cholesterol (a fat carried in the blood) when compared to a higher fat intake. However, these effects varied over time with some results showing that a lower fat intake may make little or no difference. Evidence from one trial suggested that lower fat intake probably had no effect on blood levels of one type of cholesterol (called HDL‐cholesterol) and may have no effect on height compared to higher fat intakes. This evidence cannot necessarily be applied to all healthy children, as two studies were done in children with raised blood cholesterol levels.
We also looked at 21 studies in approximately 25,059 children that observed and measured the children's intake of fat and their weight, BMI, and other body measures over time, but did not seek to directly change what they ate (these are called cohort studies). Over half of these cohort studies that reported on body fatness suggested that as total fat intake increases, body fatness may move in the same direction. However, results varied across all these studies and we could not draw any firm conclusions.
Quality of the evidence
We found no high‐quality evidence with which to answer this question. Evidence from the cohort studies was generally of very low quality so we are uncertain about these results and cannot draw conclusions. For the three randomised controlled trials, the results that we were most interested in were generally of moderate‐ or low‐quality evidence. We could not make any conclusions about children in low‐ and middle‐income countries as 23 of the 24 studies were done in high‐income countries. More high‐quality, long‐term studies are required that also include children from low‐ and middle‐income settings.