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Most people know that consuming too much fat, and especially saturated fat, is bad for your health. That’s why there has been a concerted push for several decades to get people to reduce the amount of saturated fat that they consume, and to replace it with complex carbohydrates. Now unfortunately people often misinterpret that to mean that fat is evil, but carbs are ok. This is problematic since consuming too many simple carbs is also likely to increase the risk of obesity, diabetes, and cardiovascular disease – exactly what we are trying to prevent in the first place. So this raises the important question – in order to minimize the risk of heart disease, is it better to reduce the intake of saturated fat, or the intake of simple carbs? An interesting new study in the American Journal of Clinical Nutrition examines this issue and while it doesn’t provide a definitive answer, it suggests that refined carbs are pretty bad indeed.
The new study was performed by Marianne Jakobsen and colleagues at the Aarhus University Hospital in Denmark, and it has a massive sample – 53,644 healthy men and women. At baseline (from 1993-1997) these individuals completed a detailed questionnaire regarding their diet, physical activity levels, and other health-related variables including smoking status and socio-economic status. These individuals were then followed until they had a heart attack, died, emmigrated, or until the end of the study in April of 2008 – whichever came first.
Using the diet questionnaires, researchers calculated both the amount of saturated fat and carbohydrate in the diet, as well as the quality of the carbohydrates being consumed. This was done using the glycemic index, which measures the impact of a given carbohydrate on blood sugar levels. For example, sugar and white bread are foods with a very high
glycemic index, vegetables like carrots or onions have a very low glycemic index, and foods like raisins and shredded wheat fall somewherein the middle (more details here). What did they find?
During an average follow-up of 12 years, there were 1943 heart attacks in the study sample. Simply swapping saturated fat for carbohydrates (e.g. a 5% increase in energy intake from carbs along with a 5% decrease in energy intake from saturated fat) was not associated
with any change in risk of heart attack. However, swapping saturated fat for carbs with a high glycemic index (e.g. 5% lower calories from saturated fat, and 5% increased calories from high GI carbs) was associated with a 33% increased heart attack risk.
Now I should mention a few things up front. There was no intervention here, so people didn’t actually swap saturated fat for carbs for saturated fat – this was all calculated statistically. That doesn’t mean I would discount these findings, but I think it’s worth mentioning. Also, diet was assessed once, using self-report, so it would be interesting to see if a similar study with a bit closer monitoring shows similar results. The authors also mention several times of the “nonsignificant inverse association” between low-GI foods and heart attack risk (HR = 0.88, .72-1.07). With 50,000+ people it’s hard to argue that this study was under-powered. But as I mentioned the measures of diet weren’t ideal, and this is where I think another study
with more direct measurement could be of real use.
So what’s the take home message?
Previous studies have suggested quite clearly that consuming too much saturated fat is a bad thing. But not surprisingly, swapping out that saturated fat for carbs with a high glycemic index isn’t such a great move either – it’s essentially trading one crappy food for another. Frank Hu lays out an excellent prescription in an accompanying editorial. In it, he suggests that excessive intake of refined carbs (and especially sugar-sweetened beverages) represent the “perfect storm” for increasing risk of chronic diseases. Fortunately, he points out that many dietary strategies can reduce the intake of refined carbs – for example:
…replacing carbohydrates (especially refined grains and sugar) with unsaturated fats and/or healthy sources of protein and exchanging whole grains for refined ones…
limiting sugar-sweetened beverage consumption, a major source of dietary [glycemic load] and excess calories, has been associated with lower risk of obesity, type 2 diabetes, and IHD.
A very-low-fat, high-carbohydrate diet (eg, percentage of energy
<20% from fat and >70% from carbohydrates), once typical in traditional Asian populations, has the potential to be cardioprotective if most of the carbohydrates come from minimally processed grains, legumes, and vegetables and if the population is lean and active (and thus has low insulin resistance)…
a diet with moderately restricted carbohydrate intake but rich in vegetable fat and vegetable protein improves blood lipid profile and is associated with lower risk of IHD in the long term.Benefits of the plant-based, low-carbohydrate diet are likely to stem from higher intake of polyunsaturated fats, fiber, and micronutrients as well as the reduced GL in the
So it really comes down to what
many people have been saying all along – aim for a diet high in plants,
low in refined foods and saturated fat, and limit your intake of sugary
beverages. And if you’re trying to reduce the amount of saturated fat
in your diet, make sure you’re not simply replacing it with refined
Hu FB (2010). Are refined carbohydrates worse than saturated fat? The American journal of clinical nutrition, 91 (6), 1541-2 PMID: 20410095
Jakobsen MU, Dethlefsen C, Joensen AM, Stegger J, Tjønneland A, Schmidt EB, & Overvad K (2010). Intake of carbohydrates compared with intake of saturated fatty acids and risk of myocardial infarction: importance of the glycemic index. The American journal of clinical nutrition, 91 (6), 1764-8 PMID: 20375186