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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This post is just what i needed. so refreshing(while not really based on the reporting)… i just cant stand how the CORRECT studies are never performed nor published well.
This seems to be yet another study which takes a reductionist approach – counting ‘food’ in terms of carbohydrate and fat.
The important thing is to eat real WHOLE unrefined, unprocessed foods – fresh fruit and vegetables, nuts, seeds, herbs, spices, sea fish, wild animal foods and some whole grains. If one does this the issue of low, medium or high-GI carbs versus saturated fat does not exist. Natural foods, viewed in reductionist terms, ‘contain’ carbs, proteins and fats in natural proportions which the body can handle and thrive upon. It is only refined and processed foods (such as white bread and sugar) and intensively farmed animal foods (such as from grain fed animals) that ‘contain’ unfavourable types and proportions of carbs, proteins and fats.
In summary, the work reported sounds like comparing MINOR variations in an unnatural diet and does not address the core problem of ‘natural’ food versus ‘refined and processed’ food.
Dr. Briffa,
Thanks for looking deeper into this study and extracting the truth of the findings for us. Very little frosts me more than to see a study where the abstract and/or the results do NOT match with the data found in the body of the study.
In our modern society most of us look (at least in part) to “science” to help us understand what is going on and what is the “truth”. This type of behavior casts doubt on the general trustworthiness of the scientific literature.
I’m sure you have already, but I would direct your readers who have interest in this to look into the work of Uffe Ravnskov. He has systematically evaluated most of the studies that “prove” that saturated fat is bad and found that many follow the same tact as the paper you cited, where the data does not actually support the conclusion that saturated fat is bad.
Thanks again for the post.
Regards,
Dr. Tim Gerstmar
Great post John. Very interesting conclusion the authors came to indeed.
“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.”
Based on the 95% confidence interval, with the upper end at 1.07, we could also say that”replacing SFA’s with carbohydrates with low-GI values is associated with a higher risk of MI…”
And using that same 95% CI, there is a 2.5% chance that replacing SFA with low GI CHO would increase the risk of MI by more than 1.07 (relative risk).
I guess I would find anything about this study more meaningful if we knew what was the actual effect of the foods eaten- i.e., the combination of foods can affect the blood glucose effect in addition to any inherent low or high GI effects. Eating a grilled cheese sandwich does not have the same effect on blood glucose as eating a couple pieces of toast, even though the same amount of carbs are consumed. At least there is some questioning of dogma in this study, though not enough.
Very interesting post.
By the way, have you read this recent study:
http://www.cell.com/trends/endocrinology-metabolism/fulltext/S1043-2760(10)00023-8
What is your view on this? Could they be right?
I just feel that it is sad how little the public know about healthy eating and , dare I say it, especially men. As a nutritionist I see many professional and well educated people who are wizards in their difficult jobs but know nothing about nutrition and so are easily bamboozled by the food industry.
If anyone saw the programme ‘Super fat and Super skinny’ where a doctor was giving them a ‘healthy’ breakfast. It was ALL carbohydrate-fresh orange juice, cereal, toast, strawberries. (a little protein in the milk). Hilda
“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.”
Now now, Dr Briffa, you mustn’t lay the blame for the misinformation on ‘old wives’…(o: – It’s doctors and nutritionists et al who have been misinforming us about saturated fats, not ‘old wives’ (who were also blamed, I noticed, for warning people not to eat many eggs, when again, it was the health professionals who had given the unjustified warnings about eggs and cholesterol. ‘Old wives’ were completely innocent; in fact they always told us that eggs were good for us.)
Thank you for another very interesting blogpost.
So similar to the Man-Made Global Warning scares -don’t let the science get in the way of the story: just say it’s “settled” and move on.