Saturated fat - all change for healthy eating?
The media has had a field day. Banner headlines have been screaming that saturated fats aren't bad for you after all, and that scientists and doctors have been giving us the wrong advice for years. So what should we believe?
For years, national and international guidelines have urged us to cut down our intake of saturated fats - found largely in high-fat dairy foods and fatty meat - and switch to unsaturated versions found in plant and fish oils. Now a major review of 72 studies, which included over 650,000 people, has compared populations with high and low (top 1/3 and bottom 1/3 in terms of intake) consumption of saturated and various kinds of unsaturated fats. It suggests that a high intake of saturated fat does not increase the risk of heart disease and eating more polyunsaturated fat doesn't lower it.
There are limitations to the research:
- With such a large number of different studies, the populations might not be comparable, increasing the chance that other 'confounding' factors might account for some of the findings.
- Some of the studies depended on diet questionnaires. Studies which depend on what people remember about their lifestyle are notoriously inaccurate, and diets often change over the long term.
- The results only look at fat intake, not other aspects of diet and lifestyle. For instance, if the people with low intake of saturated fat were eating large amounts of other refined foods in their place (and we know this often happens), their diet might have been just as 'heart unhealthy' as those eating more saturated fat.
- The studies looked at people who already had existing health conditions. It's not clear if the same results would have been found in healthy populations.
The study does confirm one piece of advice we have been giving for years - trans fats are bad for your heart. Doctors and dieticians have been warning of their danger for years, and as a result most margarine manufacturers have dramatically reduced the amounts they use, or cut them out entirely. However, they're still found in many shop-bought pastries, cakes, pies and biscuits. Trans fats as such don't need to be included in the ingredients on food labels, but most products with 'partially hydrogenated oils' (which do have to be listed) contain trans fats. The higher up the list of ingredients, the higher the levels. (2)
So where does this leave us? Can we start deep-frying Mars® bars without a murmur of conscience? Er, no. Even if saturated fat in itself isn't bad for your heart (and the authors are calling for more detailed research to look specifically into this), all fats are high in calories, and too much of them in your diet means you are almost bound to put on weight. Nobody is arguing that being obese doesn't have risks - type 2 diabetes, and yes, heart disease and stroke.
This research isn't saying that eating saturated fat is good for you, just that it may not be worse for your heart than eating the same number of calories in unsaturated fat.
What's more, most of the other healthy eating messages still apply. Doctors had already been recommending a 'Mediterranean diet' for years before a major study last year showed that a Mediterranean diet supplemented by nuts or olive oil could cut the risk of heart attack by almost a third. (3)
The people in this study who cut their risk of heart attack were eating everything in moderation - apart from vegetables, where a 'the more, the better' rule applies. You need the 'whole package' of balanced healthy eating - the diet used in this study included three servings a week of nuts, five portions a day of fruit and veg, three portions a week of fish (especially oily fish), four tablespoons a day of olive oil, less than one serving a day of red meat and limited pastries, cakes, butter, spread fats and fizzy drinks. The only element of this diet that has been called into question is the olive oil.
Am I changing my diet on the basis of this week's headlines? Categorically not.
3. Estruch R et al. Primary prevention of cardiovascular disease with a Mediterranean diet. NEJM 2013 http://www.nejm.org/doi/full/10.1056/NEJMoa1200303