Whether the amount of fat we eat affects our weight has been a hot topic of debate for years. Now, an analysis of the research finds that fat matters, and just switching higher-fat foods for their lower-fat counterparts – without any other dietary change – can help dieters lose a modest but significant amount of weight.
The study was published online in BMJ.
For the analysis, researchers looked at the 43 studies that compared a group of people who ate a low-fat diet to those eating the usual amount of fat. Thirty-three of those studies were randomized controlled trials (RCTs), lasting from six months over eight years and including almost 75,000 people.
RCTs are considered one of the strongest types of studies, randomly giving one group the dietary intervention and then tracking all involved.
None of the studies focused on weight loss because the researchers were not trying to find the effects of dieting, says Lee Hooper PhD, SRD, of UEA’s Norwich Medical School and the lead researcher of the study. Instead, studies were focusing on other outcomes, such as high blood pressure or cholesterol. But all the studies measured their participants’ body fat, such as weight and waist size, at the beginning and end.
The analysis of the 33 RCTs suggested that diets lower in total fat on average reduced body weight by about 3.5 pounds – 1.6 kilograms. Those eating a low-fat diet also had a smaller waist of about a tenth of an inch, 0.3 centimeters. The weight loss occurred early and was maintained over at least seven years.
Each one percent decrease in calories from total fat resulted in a 0.19 kg – almost half a pound – reduction in body weight, compared with not altering total fat intake. If you were on a 2000-calorie diet, that decrease translates to exchanging a full-fat cup of milk to the 2 percent – a savings of about 20 calories.
The evidence was remarkably consistent, noted Hooper. And what was most interesting is that these people were not trying to lose weight, which shows that choosing to eat sensibly can lead to sustained weight loss (over at least 7 years). “If people choose to reduce their fat and eat a little less then the effects are likely to be more dramatic – but this is only worthwhile for health if the effects are sustainable over time,” said Hooper.