The debate about fat has raged since the 50’s when Ancel Keys, one of the first researchers to examine the cardio-protective properties of the Mediterranean diet, launched the mammoth 7 Countries Study. The main hypothesis to be tested was that the rate of coronary disease in populations and individuals would vary in relation to the fat composition of their diet, and to their serum cholesterol levels.
This was one of the first major attempts to link diet to disease risk, and it is no exaggeration to say that we are still living in Ancel’s shadow; a good deal of nutritional research and advice still revolves around dietary fat. And it is true that there is a correlation between saturated fat intake and serum cholesterol levels. There is also a (slightly shaky) correlation between cholesterol levels and heart disease. But, but, but … correlation does NOT equal causation, and it is not at all clear that eating a diet rich in saturated fat automatically raises your risk of heart disease.
Eating, after all, is a zero sum game. If you are eating more fat (and sugar – the two often go together, especially in the processed and ultra-processed foods that have become such a predominant part of our diet), you are eating fewer foods that contain the key cardio-protective compounds.
In particular, you are almost inevitably consuming insufficient omega 3 fatty acids (from oily fish), and insufficient polyphenols (from plant foods) to prevent chronic inflammation from occurring in the body. Once you have chronic inflammation, things start to go wrong.
The extra-cellular matrix that gives structure and function to all your tissues erodes, forming micro-ulcers in tissues such as the linings of the blood vessels. Into these sites of micro-damage pour immune cells such as macrophages, as part of the inflammatory response; and once inside the arterial walls those cells die, producing growing pockets of oxidized cholesterol. The processed food diet is not only pro-inflammatory, it is also depleted in key antioxidants, and this means that lipids and cholesterol in the blood stream, and probably elsewhere in the tissues, are prone to oxidation.
The oxidized and highly pro-inflammatory cholesterol sludge in atheroma comes primarily from the dead macrophages, not from serum cholesterol directly. This is one reason why serum cholesterol is such a poor biomarker for heart disease; and one reason why high blood pressure is linked to coronary artery disease, because both are driven by chronic inflammation. (When chronic inflammation occurs in the arterial walls, it is termed ‘endothelial dysfunction’).
So even if a diet rich in saturated fat and cholesterol does increase the risk of heart disease, the causative link may not only be what this diet contains, but also what this diet does NOT contain.
There was fierce argument between Keys and the British physiologist and nutritionist John Yudkin, who believed that sugar was more dangerous than fat. Yudkin’s theories about the role of sugar in causing coronary heart disease were overcome by Keys’ ideas at the time, because Keys had access to more funding, and produced a higher quality of data. But although Yudkin died a broken and forgotten man, I think he was probably right, at least in part. In fact I think that Yudkin and Keys were both partly right, and that the debate – which was highly adversarial – should have been a synthesis, and probably would have been had Keys been more generous.
A diet high in sugar (which as I suggested above is also likely to be high in fats, and low in protective anti-inflammatory nutrients), creates glycative stress, and acts via the AGE-RAGE interaction to cause chronic inflammation generally, and endothelial dysfunction in the arterial network. This drives heart disease.
A diet high in saturated fat and cholesterol (which is also, in these benighted times, overwhelmingly likely to be rich in sugars and low in anti-oxidant nutrients), produces raised levels of fats and cholesterol in the blood, which are unprotected from oxidative stress and therefore prone to forming lipid and cholesterol oxidation products. These, too, cause chronic inflammation, endothelial dysfunction and heart disease. They are picked up by the same macrophages that migrate into sites of vascular damage, die, and deposit the oxidized cholesterol sludge that forms much of atheromatous plaque.
From this perspective, some of the latest research begins to make more sense.
For example, a study reported just last week (1) that saturated fats in yoghurt, cheese and butter do NOT increase the risk of heart disease – and appear to reduce the risk of dying from stroke by a striking 42%.
Dairy foods contain saturated (and omega 6) fatty acids, and according to the Keys hypothesis would be expected to increase risk; but at the same time, dairy foods tend to be low in sugar (except for those disgusting sugar-sweetened yoghurts). And they are good sources of calcium, which does not protect your bones but can help to lower blood pressure. Now here is the interesting part. Dairy foods have anti-inflammatory effects in the body (2-4), which are probably mediated by the amino acid leucine. And if you are eating more dairy (ie relatively unprocessed foods), you are likely to be eating other unprocessed foods such as fruits, vegetables and whole grains, which contain other anti-inflammatory compounds such as the polyphenols.
This recent study was rather robust. The researchers, from the University of Texas, Houston, analysed nearly 3,000 adults aged over 65 for 22 years. The participants’ plasma was assessed to determine different levels of fatty acids in 1992, and then again six and 13 years later. And the level of risk reduction was, at 42%, highly significant.
In addition to this recent finding, we should consider the historical angle. Back in 19th century England the population consumed far more saturated fat than we do, in meat and dairy, but very little sugar – and their level of heart disease was around 10% of today’s values (5).
So what is my position?
I believe that neither saturated fat nor any other kind of fat is intrinsically unhealthy, except of course the industrially produced trans fats (6, 7) which should be universally banned. I think that excessive amounts of sugar, especially when combined with today’s low energy lifestyle, are generally unhealthy.
And it is very clear that the modern, processed and pro-inflammatory diet, which is depleted in omega 3’s and polyphenols and most other micro- and phyto-nutrients besides, leaves us all vulnerable to degenerative disease in general and cardiovascular disease (and cancer) in particular.
If we are serious about improving public health we need to move on from a myopic obsession with single agents such as saturated fat and/or sugar, to a multi-variable approach to the incredibly complex interaction between diet and health.
Cutting down on processed and ultra-processed food is a good start, and 5-a-day is a reasonable second step. But to achieve radical improvements, we need to transform our excessively and dangerously pro-inflammatory food universe into a moderately anti-inflammatory one. You could wait for the spavined and bought political creatures in Brussels, Berlin, Whitehall and Washington to do this. More realistically, you can create an anti-inflammatory environment inside your own body – and at this time, a well-designed omega 3 / lipophile polyphenol supplement is the most effective way of achieving this.
de Oliveira Otto MC, Lemaitre RN, Song X, King IB, Siscovick DS, Mozaffarian D. Serial measures of circulating biomarkers of dairy fat and total and cause-specific mortality in older adults: the Cardiovascular Health Study. Am J Clin Nutr. 2018 Jul 11. doi: 10.1093/ajcn/nqy117
Zemel MB, Sun X, Sobbani T, Wilson B. 2010. Effects of dairy compared with soy on oxidative and inflammatory stress in overweight and obese subjects. American Journal of Clinical Nutrition 91: 16-22.
Pei R, DiMarco DM, Putt KK, Martin DA, Gu Q, Chitchumroomchokchai C, White HM, Scarlett CO, Bruno RS, Bolling BW. 2017. Low-fat yogurt consumption reduces biomarkers of chronic inflammation and inhibits markers of endotoxin exposure in healthy premenopausal women: a randomized controlled trial. British Journal of Nutrition 118: 1043-1051.
Labonte M-E, Couture P, Richard C, Desroches S, Lamarche B. 2013. Impact of dairy product on biomarkers of inflammation: a systemic review of randomized controlled nutritional intervention studies in overweight and obese adults. American Journal of Clinical Nutrition 97: 706-717.
Clayton P, Rowbotham J. How the mid-Victorians worked, ate and died. Int J Environ Res Public Health. 2009 Mar;6(3):1235-53.
Ganguly R, Pierce GN. The toxicity of dietary trans fats. Food Chem Toxicol. 2015 Apr;78:170-6.
Ganguly R, LaVallee R, Maddaford TG, Devaney B, Bassett CM, Edel AL, Pierce GN. Ruminant and industrial trans-fatty acid uptake in the heart. J Nutr Biochem. 2016 May;31:60-6.