Lipids Suffer When Less Saturated Fat in Diet Is Replaced by Carbs in Worldwide Study

Marlene Busko

June 09, 2016

MEXICO CITY, MEXICO — An analysis of how carbohydrate and fat intake affects blood lipid profiles in more than 100,000 individuals living in 19 low- to high-income countries suggests that the message to lower dietary saturated fats to lower cholesterol and thus decrease risk of cardiovascular disease may be misleading[1].

The danger lies in replacing saturated fat with carbohydrates, according to findings from the Prospective Urban Rural Epidemiological (PURE) study, which Dr Mahshid Dehghan (McMaster University, Hamilton, ON) presented on June 6, 2016 at the World Heart Federation's World Congress of Cardiology & Cardiovascular Health 2016 (WCC 2016).

"With a high-carbohydrate diet, you lower your total cholesterol and your LDL cholesterol, but you decrease your HDL cholesterol and increase your total cholesterol/HDL ratio and your apolipoprotein-B (apoB)/apoA ratio (which seem to be better markers to predict risk of cardiovascular disease), and you also increase your triglycerides; therefore, we see there is more harm," she reported.

However, replacing saturated fat with monounsaturated fatty acids (MUFAs) had beneficial effects only on lipid profiles and replacing it with polyunsaturated fatty acids (PUFAs) had mixed benefits and harms, in their modeling analysis.

"When we encourage people to lower their fat, by default they increase their carbohydrate consumption, and we will not see a reduced risk of cardiovascular disease by this approach," Dehghan told heartwire from Medscape.

It's very simplistic to look at only one marker of blood lipids; it's more complex than that, she added. According to Dehghan, "It's better to encourage people to have a healthy diet that is high in fruits, vegetables, and legumes than just emphasizing lowering saturated fat." Their findings also support the benefits of a Mediterranean diet, which includes olive oil and nuts, she noted.

Effect of High-Carb vs High-Fat Diets on Blood Markers

Reducing intake of saturated fat while upping intake of carbohydrates to reduce total blood cholesterol levels and presumably CVD "has recently been challenged, and there are no data from low- and middle-income countries where >80% of CVD occurs," Dehghan and colleague write.

To investigate the effect of nutrients on blood lipid levels, they examined data from the PURE study, from 145,275 participants who had replied to a food frequency questionnaire and 113,876 participants who had blood lipid levels measured.

With a high-carbohydrate diet, as suggested by the World Health Organization (WHO), their analysis showed that the only benefit was that total cholesterol and LDL cholesterol dropped, but there were many harmful effects on other blood lipids: HDL-cholesterol and apoA levels decreased, while triglycerides and the ratios of total cholesterol/HDL cholesterol and of apoB/apoA increased.

With a high–saturated-fat diet, the only harm was increased LDL cholesterol, but on the other hand there was a benefit of reduced triglycerides.

With high MUFA consumption, there were beneficial effects only on blood lipids: HDL cholesterol increased, and triglycerides and the ratios of total cholesterol/HDL and apoB/apoA decreased.

With high PUFA consumption, there was a mixed effect: apoA decreased (which is harmful), but because apoB decreased as well, the ratio of apoB/apoA decreased also (which is beneficial).

Nutrition guidelines recommend that 60% of calories should come from carbohydrates and only 5% to 6% of calories from saturated fat, but they place "more emphasis on saturated fat—'saturated fat is evil'—and we forget about carbohydrates," Dehghan told heartwire .

"Therefore, maybe it's very simplistic to see the effect of saturated fat on only one marker—total cholesterol. We may need to change the message and bring more awareness about carbohydrates, not emphasis on saturated fat, because study after study shows that saturated fat is not that bad," she added.

However, they are not suggesting that people should up the intake of saturated fat from the current recommended 5% to 6% of calories to 15% of calories, she cautioned. And when it comes to carbohydrates, moderation is the best; the study suggests that "45% to 55% of energy from carbohydrates might be good," she said.

"To summarize our findings, the most adverse effect on blood lipids is from carbohydrates; the most benefit is from consumption of monounsaturated fatty acids; and the effect of saturated and polyunsaturated fatty acids are mixed. I believe this is a big message that we can give because we are confusing people with a low-fat diet and all the complications of total fat consumption, and WHO and AHA all suggest 55% to 60% of energy from carbohydrates."

An audience member wanted to know if the study found any evidence of a shift to more processed foods, even in low- and middle-income countries. Dehghan replied that they did find this, adding that low-income families mostly consume refined carbohydrates (the worst kind) and don't consume whole grains.

Study Supports AHA Guidance on "Good" vs "Bad" Fatty Acids

According to the AHA website, foods that are high in polyunsaturated fat include plant-based oils (eg, soybean, corn, and sunflower oil), fatty fish (eg, salmon, mackerel, herring, and trout), some nuts and seeds (eg, walnuts and sunflower seeds), tofu, and soybeans. Foods that are high in monounsaturated fats include plant-based liquid oils (eg, olive, canola, peanut, safflower, and sesame oil), avocados, peanut butter, and many nuts and seeds. Saturated fats are found in meat and dairy products (eg, fatty beef, lamb, pork, poultry with skin, beef fat [tallow], and lard as well as cream, butter, cheese, and other dairy products made from whole or 2% milk), many baked goods and fried foods, and some tropical oils (eg, palm, palm kernel, and coconut oil).

"You should replace foods high in saturated fats with foods high in monounsaturated and/or polyunsaturated fats. This means eating foods made with liquid vegetable oil but not tropical oils. It also means eating fish and nuts. You also might try to replace some of the meat you eat with beans or legumes," the website advises, which agrees with the findings of the current study.

The study authors declared no relevant financial relationships.

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