The sugar-carb-fat wars - who's right?
Earlier this year, we saw banner headlines about how saturated fat had been the victim of a systematic witch hunt by the establishment for decades. Instead, all the time we should have been focussing on sugar as the bad guy - in fact, fry-ups were back on the menu for good health.
I was not convinced. It's not that I believe sugar is blameless - anything but. Sugar is worse than just completely empty calories - it is actively damaging to our health, and has undoubtedly played a huge part in our current worldwide epidemics of obesity and type 2 diabetes. In fact, there is emerging evidence that even low calorie sugar substitutes might not be the guilt-free alternatives we have all believed for so long.
But the evidence against saturated fat is damning. Earlier this year, the World Health Organization published a 72-page report examining reams of evidence (and including evidence from 84 studies) of the effect of saturated fat on cholesterol levels. It concluded that replacing saturated fats with unsaturated (particularly PUFA, or polyunsaturated fats) improved total cholesterol, 'bad' LDL cholesterol and triglyceride levels. Replacing sat fats with PUFAs was more effective at reducing lipids than replacing them with a mixture of carbohydrates - including refined carbohydrates, of which sugar and white flour are the most commonly eaten examples.
Thousands of studies on millions of patients have shown a clear link between cholesterol levels andrisk of heart attack and stroke. But getting studies that show definitively that any one food causes heart attacks and strokes is challenging. For a start, the 'gold standard' for a clinical trial is a double blind trial - where two options are compared, and neither the patient nor the investigators know what group the patient is in. Most people would realise if they were randomly assigned to the Full English or the porridge-and-nuts group. Secondly, it takes weeks or months for your cholesterol to change - but decades before enough people have heart attacks for a difference to show.
That's where so-called 'observational studies' come in. Last year saw the publication of study which followed 127,000 men and women over 24-30 years. It showed replacing 5% of saturated fat in the diet with the same calorie equivalent of PUFAs was associated with a 25% lower risk of heart disease. For wholegrain carbohydrates, the figure was 9% - but substituting refined carbohydrates for saturated fat didn't reduce the risk of heart attack and stroke at all. Today, a further analysis looks at the individual sources of saturated fat (lauric, palmitic, stearic, myristic acids) and shows a similar picture. It also shows that the benefits don't just apply to unsaturated fats and wholegrain carbohydrates - replacing sat fats with plant proteins also cut the risk of heart disease.
And that's what makes this study so interesting to me. It's not about what you cut out, it's about what you replace it with - and it's about the bigger picture diet-wise. We really should have learnt that by now. As the editorial that accompanies the paper points out, "no single observational study can tell us whether or not a single nutrient is 'harmful'".
But we do know enough about a combination of foods that our Southern European colleagues have espoused for years. The Mediterranean Diet, with its strong evidence for heart protection, isn't about one food. It's about a combination of lower dairy products, red meat, processed meats, and sweets and higher veg (including tomatoes, garlic and onions)/fruit/unrefined carbohydrate/fish/nuts/olive oil. It ticks all the boxes in today's study - unsaturated fats, plant protein and unrefined carbohydrates - and it works. So let's stop focussing on sugar or saturated fat as the bad guys. Let's accept we should be viewing them both with caution, and looking at what we do eat as well as what we don't. We owe it to our hearts.