The recommendations to move to a low fat diet were based on inconclusive evidence. That is the finding from a review published in the OpenHeart journal.

The review investigates the evidence that was used as the basis of the recommendation to reduce total fat intake to 30% of energy intake and to reduce saturated fat intake to 10% of energy intake. The recommendations were adopted by the US government in 1977 and applied to 220 million US citizens.

The shaky link between low fat and heart health

The recommendations to reduce fat in the diet were taken as a measure to reduce rates of heart disease, which had grown to be a major cause of death by the 1970s. Prior to 1977, studies, such as the Seven Countries Study, which was carried out by University of Minnesota researcher Ancel Keys, had shown a strong association between high cholesterol levels, obesity and increased rates of heart disease.

A further association was made between high cholesterol levels and high fat intake, however, the association was not rigorously tested using randomized controlled trials. The review in the OpenHeart journal notes that the quality of evidence available to make the low fat diet recommendations was poor and based upon secondary studies of just 2,467 males. Furthermore, these dietary studies failed to show any significant decrease in coronary heart disease (reduced risk of 1.1%) or all-cause death rates (reduced risk of 0.4%).

The review notes that the figures of 30% total fat intake and 10% saturated fat intake were arbitrary and untested by any prior clinical trials. Research has consistently shown, particularly within the last decade, that any high calorie diet, be it from high fat intake or high carbohydrate intake, raises cholesterol levels and most notably triglyceride levels.

Consequences of low fat diets

One of the consequences of a the low fat recommendations was that processed foods began to dominate the US diet. Our went saturated fat and in its place came higher amounts of sugar and of trans fats.

Trans fats allowed food manufacturers to take polyunsaturated fats, treat them with hydrogen and create a similar texture as saturated fat whilst meeting government recommendations. Eventually, trans fats were shown to be a flawed idea and, in fact, far more dangerous to health than saturated fat. After being present in the US diet for more than a century, in 2013 the FDA finally recognised that trans fats are not ‘generally recognised as safe’.

The other major dietary winner from low fat diets was sugar with a whole range of ‘diet’ products claiming to be ‘low fat’ whilst boosted with added sugar.

Low fat diets and diabetes

The change towards low fat diets has had particular implications for people with diabetes as diet, in all main types of diabetes, is recognised as an important part of diabetes control. The move towards low fat diets saw people with diabetes being advised to ensure they ate a significant proportion of their energy intake from carbohydrate.

A problem that has arisen is that higher carbohydrate intake leads to higher HbA1c levels and/or greater dependence upon medication to control blood glucose levels.

Healthy fats

Modern research is turning the idea that fat is inherently bad on its head. Direct comparisons of low carbohydrate diets with equal calorie low fat diets have shown low carbohydrate diets to be at least as healthy as low fat ones with low carbohydrate diets showing particular benefit for people with diabetes.