Fats & oils
Governments and public health bodies have, for almost as long, shaped many of their recommendations around that thinking. Yet there is a – growing – cohort that contests it; with the debate arguably more hotly contested now than ever before. It’s important to note that the picture is far more multifaceted than that of industrial trans fats, which have largely been removed from our diets.
Professor Nita Forouhi of the University of Cambridge offers a considerably more straightforward perspective of where our understanding of fats in the diet, especially saturated fats, is than some of the scientific literature: “There is plenty of evidence that industrial trans fats are ‘bad’ for health, to the extent that zero intake is best, and that unsaturated fats are ‘good’ fats and should be increased in the diet.” Acknowledging the ongoing debate, the physician scientist and specialist in nutrition and epidemiology says the dial has shifted in regard to saturates. “Saturated fats can be thought of as being ‘in-between’ good and bad fats,” she says. The main principle, according to a swathe of public health guidance, is to keep your saturated fat intake to below 10% of your total energy intake per day. On this Dr Frank Hu, a professor of nutrition and epidemiology at Harvard University, and Forouhi agree. But as Hu notes, it’s a little more complex. He says there are two issues: the effects of saturated fat depend on the comparison macronutrient; and saturated fat is heterogeneous in terms of types and food sources. He believes that if saturated fat is compared with healthy fats like mono or polyunsaturated fats (MUFAs or PUFAs), or fibre-rich carbohydrates like whole grains, it poses a cardiovascular (CVD) risk. However, if it is compared with refined carbs or sugars the risk is comparable. “Some saturated fats, like stearic acid, do not increase blood cholesterol,” he says. “However, most long-chain saturated fats like lauric acid, myristic acid, and palmitic acid do raise LDL [low-density lipoprotein] cholesterol and increase the risk of CVD. These saturated fats primarily come from meats, dairy, and tropical oils.”
Complexities of saturated fatty acids and impacts on health Saturated fatty acids (SFAs) vary in their biological properties, depending on the number of carbon atoms in the fatty acid chains. Forouhi says the research she has been involved in shows that different SFAs are related differentially with health outcomes such as Type 2 diabetes and CVD. For instance, SFAs with an odd number of carbon atoms – c15:0 and c17:0, for example – are related inversely with the risk of future Type 2 diabetes, whereas those with an even number are related positively with risk.
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Herein lies the challenge for public health bodies, consumers and food manufacturers. Whilst Hu identified some of the LDL challenges posed to our bodies by certain foods, and of course his assertions are based on scientific fact, Forouhi adds a further layer of complexity. In essence, she says in certain food subgroups SFAs have differing effects. For example, red meat and dairy are both high in saturated fat, but they have different disease risks. “Meat is positively associated, that is higher consumption is linked with higher risk,” she explains, “while certain forms of dairy, particularly fermented dairy – yoghurt and cheese, for example – are inversely associated; so higher consumption is linked with lower risk of cardiometabolic disease.” It’s a point supported by a growing body of research.
Shifting perspectives and the importance of context So, when it comes to saturated fats the message is clear-ish. What we first believed to be wholly bad fats are perhaps not quite as much of an enemy to health. In recent years, several studies have supported that. With conclusions ranging from overall saturated fat does not pose a danger to health, it’s the foods high in it that do, to there being no evidence that cutting saturated fat from a diet can improve health and reduce the risk of disease, and even saturated fat intake can actually reduce the risk of certain disease in women, it seems the debate endures. However, both Hu and Forouhi caution against taking one or a few studies in isolation. “Several years ago, there were sensational headlines like ‘butter is back’,” says Hu. “However, the effects of saturated fat depend on the replacement macronutrients. He says some studies that found no harmful effects of saturated fat essentially compared it to carbohydrates, many of which are of poor quality in our diets. Forouhi is as direct: “The human diet and its health effects are complex. Reductionist messages that single out a single diet factor as the culprit or the magic bullet solution are unhelpful.”
There are, though, good fats that can be considered as alternatives. “Fats are of different types,” Forouhi says. “There are good fats like unsaturated fats that should be consumed for good health and to replace the ‘in-between’ SFAs.” MUFAs, PUFAs and omega-3 fats are all examples of these. According to Forouhi,
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