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Research report
3 February 2014

Saturated fat

Is saturated fat really the bad guy?

For many years, public-health authorities have told us to limit our intake of saturated fat. We’ve been told saturated fat raises the total amount of cholesterol and the amount of LDL (bad) cholesterol in the blood. Saturated fats can also promote blood clotting, which can lead to a heart attack or stroke.

But recently there have been some studies and opinion pieces stating that saturated fat isn’t really the bad guy. So is it time to swap olive oil for butter? Unfortunately, for butter lovers the answer is still no.

Saturated-fat enthusiasts point to new studies supporting their position. The most recent is a systematic review and meta-analysis published in the Annals of Internal Medicine in 2014, which examined the association between dietary fatty acids and coronary heart disease. It concluded that current evidence doesn’t clearly support guidelines that encourage high consumption of polyunsaturated fats and low consumption of saturated fats.

In a letter to the New Zealand Medical Journal, Dr Simon Thornley, Professor Grant Schofield and George Henderson said this study added to the evidence that saturated-fat-based interventions should be abandoned. Dr Thornley also told us that, from an epidemiological perspective, there wasn’t strong evidence of health benefits if you swap one type of fat with another.

However, Professor Jim Mann and fellow researchers from the Department of Human Nutrition at the University of Otago criticised the review in an editorial published in the New Zealand Medical Journal. They said there were serious criticisms levelled at the paper for a number of errors and omissions, which resulted in it being revised a day after publication. The corrected version still concerns some experts – including Dr Walter Willett, Chair of the Department of Nutrition at Harvard School of Public Health. He says the paper’s conclusions about the type of fat being unimportant are misleading and should be disregarded.

Dr Willett says a central issue in the debate is what replaces the saturated fat in your diet if you reduce your intake. If it is replaced with refined starch or sugar, then the risk of heart disease remains the same. If the saturated fat is replaced with polyunsaturated or monounsaturated fat in the form of olive oil, nuts and probably other plant oils there is much evidence that the risk will be reduced.

The Ministry of Health’s Food and Nutrition Guidelines for Healthy Adults state that total fat should be between 30-33 percent of total energy intake and that saturated (plus trans fats) should be no more than 12 percent. But Professor Mann told us that nutrition authorities worldwide now regard a higher range of total fat intake as acceptable, provided it mainly comes from appropriate vegetable sources. For example, the Mediterranean diet includes up to 40 percent of energy intake from fat but the fat mainly comes from unsaturated vegetable oils. The Nordic Nutrition Recommendations have increased the acceptable upper limit of total fat intake to 35-40 percent of total energy. But it’s important to remember that fat is more energy dense than other nutrients, so it’s easier to eat more kilojoules than you need.

An opinion piece published in The Lancet in 2014 by Professor Mann and his Otago colleagues stated that whatever the total fat intake, epidemiological, experimental, and clinical trial evidence supported lowering blood cholesterol by partially substituting saturated fat with unsaturated fat.

According to Professor Mann, much of the hype for saturated fats comes from advocates of the low-carbohydrate high-fat (LCHF) diet. LCHF diets involve radically restricting total carbohydrates but not restricting foods which are high in saturated fats.

“Most of the justification for the use of LCHF diets comes from studies that have shown that people on low-carb diets lose moderately more weight than people on other diets in the first few months (around six months). However, several randomised controlled trials have shown that after 12 months or more a reduction in energy intake is the main determinant of sustained weight loss, which is more important for long-term health.”

So for people watching their weight there’s no green light to eat more saturated fats. The bottom line is that we should still reduce our saturated fat intake. But saturated fats shouldn’t be replaced by refined carbohydrates – instead, they should be replaced by healthier fats from plant oils, nuts, seeds and fish. Trans fats in manufactured foods should be eliminated as much as possible. For good health you should also eat plenty of fruit, vegetables and wholegrain cereals, and reduce your intake of sodium and free sugars.

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