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Fat and Carbohydrate Intake Affects CVD and Mortality

The pendulum has swung from too much fat to too many carbs.

The relationship between macronutrients and cardiovascular disease and mortality is controversial. Most available data are from European and North American populations where nutrition excess is more likely, so their applicability to other populations is unclear.

In the 1950s, we started to see that saturated fat was clogging our arteries and we assumed too much fat was bad, so the pendulum swung to carbohydrates. Now, the PURE study shows that obtaining the majority of one’s energy from carbohydrates may not be good either and the fat we avoided isn’t as bad as we thought it was.

Dietary intake of 135,335 individuals in 18 countries was evaluated over a median follow-up of 7.4 years in this epidemiological cohort study to evaluate the association between macronutrient intake and cardiovascular disease and mortality. There was a significant association between high carbohydrate intake and the risk of total mortality but not cardiovascular disease or cardiovascular mortality. Total fat intake and intake of each fat type were associated with a reduced total mortality risk while a higher intake of saturated fat was inversely associated with the risk of stroke. The consumption of total fats, saturated fats, and unsaturated fats did not have any significant association with either cardiovascular disease or cardiovascular mortality.

The primary outcomes were total mortality and major cardiovascular events (fatal cardiovascular disease, non-fatal myocardial infarction, stroke, and heart failure). Secondary outcomes were all myocardial infarctions, stroke, cardiovascular disease mortality, and non-cardiovascular disease mortality. Participants were categorized into quintiles of nutrient intake (carbohydrate, fats, and protein) based on percentage of energy provided by nutrients. They assessed the associations between consumption of carbohydrate, total fat, and each type of fat with cardiovascular disease and total mortality.

During follow-up, they documented 5,796 deaths and 4,784 major cardiovascular disease events. Higher carbohydrate intake was associated with an increased risk of total mortality (highest [quintile 5] vs lowest quintile [quintile 1] category), but not with the risk of cardiovascular disease or cardiovascular disease mortality. Intake of total fat and each type of fat was associated with lower risk of total mortality. Higher saturated fat intake was associated with lower risk of stroke. Total fat and saturated and unsaturated fats were not significantly associated with risk of myocardial infarction or cardiovascular disease mortality.

Global nutritional guidelines should be reviewed considering these findings, which show that high carbohydrate intake is associated with an increased risk of mortality while an increase in fat intake is associated with a reduction in mortality risk and no increase in the risk of cardiovascular disease.

Populations of low and middle income ate the largest amount of processed carbohydrates (up to 60%). These often consisted of white bread and rice. The groups that consumed >60% of their energy from carbohydrates had the highest all-cause mortality, including that from heart disease. High carbohydrate intake was associated with higher risk of total mortality, whereas total fat and individual types of fat were related to lower total mortality. Total fat and types of fat were not associated with cardiovascular disease, myocardial infarction, or cardiovascular disease mortality, whereas saturated fat had an inverse association with stroke. Global dietary guidelines should be reconsidered in light of these findings.

Too much sugar is associated with elevated triglycerides, which are made by the liver to store unused carbs and is the main cause of fatty liver. It is also associated with low HDL (or apolipoprotein A1) and a high apolipoprotein B (Apo B). This study showed that high carbs were associated with a high Apo B to Apo A1 ratio, which is a better predictor of heart disease than LDL. Apo B is the small dense LDL that is more atherogenic than the larger sized LDL. And a high Apo A1 is associated with HDL levels, which are anti-atherogenic. A high Apo B/Apo A1 ratio is bad and rises with a diet high in sugar and processed carbohydrates.

This study also showed a protective effect from all types of fat. But be careful in interpreting this information. For one, fat is dense in calories, which can lead to weight gain. Animals also store toxins in their fat. Eating a lot of animal fat, particularly from red and processed meats, is not a good idea according to the evidence. Other fats such as mono-unsaturated fat (olive oil) and polyunsaturated fat (fish, nuts and avocados) are protective.

Vegetables and fruit are good sources of carbohydrates, but these are more expensive. Our most vulnerable populations consume cheap sources of carbs, which are processed and associated with high mortality. Another study published from the PURE data showed that even small amounts of vegetables and fruit (3-4 servings a day) reduced the risk of heart disease by 24% (HR 0.76) compared with 6-8 servings that reduced it by 31% (HR 0.

Practice Pearls:

  • Total fat and saturated and unsaturated fats were not significantly associated with risk of myocardial infarction or cardiovascular disease mortality.
  • High carbohydrate intake is associated with an increased risk of mortality.
  • Too much sugar is associated with elevated triglycerides, which are made by the liver to store unused carbs and is the main cause of fatty liver.

References:

Published in Diabetes  September 06, 2017;  Dehghan M, Mente A, Zhang X, et al. Lancet. 2017 Aug 28. pii: S0140-6736(17)32252-3. doi: 10.1016/S0140-6736(17)32252-3.

Micha R, Penalvo JL, Cudhea F, Imamura F, Rehm CD, Mozaffarian D. Association between dietary factors and mortality from heart disease, stroke, and type 2 diabetes in the United States. JAMA. 2017;317(9):912-924. http://jamanetwork.com/journals/jama/fullarticle/2608221

[Epub ahead of print] http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(17)32252-3/fulltext