If you want to cut your risk of heart disease, reduce intake of saturated fat and eat more carbohydrate. That’s what most doctors, dieticians and Governments would have us believe. So it must be true, right? It’s a message we’ve heard a thousand times, so surely is based on sound science?
So what does happen when individuals follow this ‘eat less saturated fat/eat more carb’ advice? Well, one way to attempt to find out would be to monitor people’s eating habits over time, and see what relationship exists between eating habits and risk of heart attack (myocardial infarction). A study published today did just that. Its subjects were more than 53,000 individuals assessed over an average of about 12 years [1].
This study looked at not just the association between saturated fat and carbohydrate and risk of heart attack, but also the type of carbohydrate consumed. Specifically, the authors of this study looked at whether the extent to which the carbohydrate eaten disrupted blood sugar levels had any apparent impact of heart attack risk. Individuals in the study were split into three groups according to the glycaemic index of the carbs they ate (low, medium and high). Higher GI foods are generally associated with biochemical and physiological changes that have adverse effects on health.
In summary, this study found that:
Substituting low-GI carbs for saturated fat was not associated with a statistically significant risk in heart attack risk.
Substituting medium-GI carbs for saturated fat was not associated with a statistically significant risk in heart attack risk.
Substituting high-GI carbs for saturated fat was associated with a statistically significant risk in heart attack risk. Increased risk was to the tune of 33 per cent.
One of the interesting things about this study was how its authors reported the results. In their conclusion, they state: “This study suggests that replacing SFAs [saturated fatty acids] with carbohydrates with low-GI values is associated with a lower risk of MI [myocardial infarction], whereas replacing SFAs with carbohydrates with high-GI values is associated with a higher risk of MI.” The latter comment is correct. The former is not: the results clearly show no statistically significant reduction in risk with the lower-GI carbs. Even scientists, from time to time, won’t let the facts get in the way of a good story.
What the results actually suggest, however unpalatable, is this: taking saturated fat out and putting carbohydrate in its place at best will do nothing in terms of heart attack risk, and at worst actually increases risk.
Now of course this is just one study, and it’s epidemiological in nature, which means it looks at associations between things but cannot really be used to prove one thing (e.g. less sat fat, more carb) is causing another (e.g. increased risk of heart disease). However, it’s not the only study that has found such a thing. Only last year saw the publication of another study (this one, an analysis of 11 studies lumped together) which linked swapping carb for saturated fat with an increased risk of ‘coronary events’ [2].
I’ve yet to see any convincing evidence that taking conventional advice and replacing saturated fat with carb improves heart health. Evidence in this area suggests no effect or a worsening of risk. And if these broad findings reflect reality, we might ask how this can be.
Well, the explanation perhaps lies in two key facts:
1. There really is no good evidence that saturated fat causes heart disease (there really isn’t). For more on this, see here.
2. Evidence suggests that carbohydrate, and particularly relatively high-GI varieties, induce changes in the biochemistry and physiology of the body that would be expected to increase the risk of heart disease. See here for more about this.
Now, I suspect these inconvenient truths will not stop some from chanting the low fat/high-carb mantra. Not so long ago I wrote about how the UK’s Food Standards Agency’s Chief Scientist (no less) apparently sees fit to keep his own blog a largely science-free zone.
His last attempt to convince us of the ‘facts’ without science prompted a barrage of criticism which has been met, by the Chief Scientist, with nothing more than stony silence.
Now, the next time someone urges you to cut back on saturated fat and eat more carbs for the sake of your heart, I urge you to ask for the science on which this advice is based. Because from what I can tell, this oft-quoted piece of dietary dogma is nothing more than an old wives’ tale, and a potentially dangerous one at that.
References:
1. Jakobsen MU, et al. Intake of carbohydrates compared with intake of saturated fatty acids and risk of myocardial infarction: importance of the glycemic index. Am J Clin Nutr 7th April 2010 [epub ahead of print publication]
2. Jakobsen MU, et al. Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. Am J Clin Nutr. 2009;89(5):1425-32.
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