Tim Spector: Butter or margarine? Food religion challengedBMJ 2019; 364 doi: https://doi.org/10.1136/bmj.l70 (Published 08 January 2019) Cite this as: BMJ 2019;364:l70
Over a hundred academics recently signed a letter to British Journal of Sports Medicine and BMJ editors criticising them for their “pro-butter” stance and for publishing a “biased” editorial which claimed that the effect of saturated fats on cardiovascular health was grossly exaggerated. A rebuttal followed. What should have been a sensible scientific debate degenerated into a dispute over bias, integrity, and beliefs.
There is certainly a touch of the religious wars about these debates, and much of this is because of who controls the sacred nutritional guidelines. The current guidelines in the US and UK are similar. Both have areas of common consensus that few disagree with—such as eating fewer calories, eating more plants, eating less processed food, and drinking fewer sugary drinks—but when it comes to saturated fat, there is much less consensus.
The fat-diet-heart hypothesis is far from simple. The original idea that cholesterol in food was to blame for heart disease has been disproven, and replaced by the total fat hypothesis, and in turn by the saturated fat hypothesis. This is based on largely observational (and some genetic) data that low density lipoprotein cholesterol in blood is correlated with heart disease and that these levels are slightly increased as dietary saturated fat increases. Observational studies in poorer countries in different environments (such as the PURE study) have shown the opposite, however, with higher saturated fats (and dairy) associated with lower mortality. No study has successfully shown that changing to a low total or saturated fat diet can reduce heart disease or mortality, and large trials like the PREDIMED study, using high fat nuts and olive oil, have shown the opposite effects, though mainly with total fat.
Another problem is deciding what practical advice to give people, when many foods considered healthy contain some of these fats. The recommendation is that foods containing saturated fats should be replaced with either starchy foods or unsaturated fats. This means, for example, swapping butter for low fat spreads (the rebranded name for margarines). The desperate wish to have a simple message that is applicable to everybody—such as “reduce all saturated fats”—creates the problem. It ignores the complexity and quality of foods, dietary patterns, and individual food choices—and it totally neglects individual variation. Research thinking is shifting rapidly from food simply being about macronutrients and calories, to consideration of the hundreds of chemicals and metabolites that interact with each other and our bodies and our trillions of gut microbes—which are unique for each of us. Meta-analyses of epidemiological studies show that eating butter containing saturated fat does not, on average, cause harm. There are no long term data on eating modern spreads, although the early trans fat versions we were encouraged to eat were harmful for most of us.
Telling people to eat low saturated fat spreads instead of dairy may force people to consume cheap highly processed items with multiple additives and novel (interesterified) fats that we know little about. Some high quality vegetable based spreads with minimal processing may actually be healthy, but people are confused by the messages and ignore these guidelines. Unilever, the market leader, recently sold its spread business, and sales of “natural” butter are increasing at the expense of “artificial” low fat spreads.
Two things need to change. Firstly, demonising one major food group or type of fat is a mistake. Foods contain a wide range of saturated, monounsaturated, and polyunsaturated fatty acids in varying proportions, and the different fatty acids never exist in isolation, meaning fats in food can have contrasting good and bad effects on the different functionality of lipoprotein particles. Secondly, we need to say farewell, once and for all, to the idea of the “standard human.” We are more individual in our food responses than most of us believe. A recent large trial found an equal number of people responded well to a low fat high carb diet as to a low carb high fat diet for weight loss. So one size is highly unlikely to fit all.
It is dangerous to vilify doctors and scientists who criticise guidelines or question population approaches. In the past year we have seen major clinical dogmas—such as aspirin for primary prevention of heart disease or vitamin D supplementation for fracture—debunked by new data. We need critics and debate more than we need outdated inflexible guidelines.
Pass the butter—or the marg.
Competing interests: TS is a consultant to Zoe Global (involved in personalised nutrition) and author of The diet myth: the science behind what we eat, Orion 2016.
Commissioned, not peer reviewed