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After decades as a fugitive from ignorant and sometimes corrupt bureaucrats, saturated fats can come in from the cold. A new study fingers trans fats as the real culprit in heart disease.
For decades we've been told to cut back on butter, eggs, meat, and cheese for the sake of our hearts. But a new systematic review of the science proves there's no additional cardiovascular risk from eating saturated fats.
Researchers at McMaster University analyzed the results of 50 observational studies assessing the association between heart disease and either saturated or trans fats.
Their results published in the British Medical Journal (BMJ) found no clear association between higher intake of saturated fats and all cause mortality, coronary heart disease (CHD), CHD mortality, ischemic stroke, or type 2 diabetes among healthy adults.[i]
But the results told a different story for trans fats. Trans unsaturated fats are mainly produced industrially by hydrogenation of plant oils. They are used in margarine, snack foods, and packaged baked goods.
Total trans fats were associated with a 34 per cent increase in death for any reason, a 21 per cent increased risk of CHD, and a 28 per cent increase in the risk of CHD mortality.
When the researchers looked at industrial trans fats (as distinguished from natural trans fats) the risk of increased coronary heart disease rose to 42 per cent.
In addition, they linked a 2 per cent increase in calories from trans fats with a 25 per cent increased risk of CHD and 31 per cent increase in CHD mortality.
They also noted that earlier prospective cohort studies reported that substituting saturated fats for 2% of calories from trans fats would reduce cardiovascular risk by 17 per cent. Substituting monounsaturated fats reduced risk by 21 per cent and substituting polyunsaturated fat reduced risk by 24 per cent.[ii]
But natural ruminant trans fats (trans-palmitoleic acid) did not have the same risks. In fact, they were inversely associated with type 2 diabetes. Other studies show this healthy trans fat slashes diabetes risk.
Palmitoleic acid, or trans-palmitoleate, is found almost exclusively in naturally-occurring dairy and meat trans fats. Unlike industrial trans fat found in hydrogenated vegetable oils, it has not been linked to higher heart disease risk. It also has anti-microbial properties and is a key compound in cell communication.
The idea that the low-fat craze is based on flawed thinking is not new. This meta-analysis of prospective observational studies confirmed the findings of five previous systematic reviews of saturated and trans fats and CHD. Still, few mainstream dieticians recommend anything but low-fat dairy and a ban on butter.
The researchers noted that theirs is the seventh systematic review and meta-analysis of observational studies of saturated and/or trans fats and health outcomes in the past 10 years. They stressed that their results are based on observational studies, so no conclusions can be drawn about cause and effect.
Saturated fats currently contribute about 10% of calories to the North American diet. The main sources are animal products, such as butter, cows' milk, meat, salmon, and egg yolks, and some plant products such as chocolate and cocoa butter, coconut, and palm kernel oils.
The researchers did not advise eating more saturated fats based on their results. They found no evidence that eating more than 10 per cent saturated fats would have additional health benefits. (But see 10 Healthy Reasons To Eat Real Butter.)
In fact, they noted that a Cochrane review of randomized trials of reduced saturated fats found a 17% reduced risk of cardiovascular death with lower saturated fat intake.[iii]
They also suggested that one of the biggest problems with low-fat diet advice is replacement calories. If you decrease calories from fat, what kinds of calories get increased?
Studies suggest that replacing saturated fats with high glycemic index processed carbohydrates increases the risk of cardiovascular disease. But replacing fat with low glycemic index carbohydrates like whole versions of fruits, vegetables, legumes, and grains decreases the risk.[iv]
The authors expressed concern about the dietary guidelines now under consideration at the USDA. Currently the guidelines recommend limiting saturated fats to less than 10 per cent of calories for most Americans. And total fat is limited to 35% of daily calories. That may change this year.
The Dietary Guidelines for Americans Committee (DGAC) is a group of independent scientists convened by the federal government to review current scientific and medical literature on nutrition. In February 2015 they issued a technical report which did not propose any restrictions on total fat consumption.
Other scientists recently urged the USDA to adopt the same position and drop all limits on the fat recommendations.
In an opinion published in the Journal of the American Medical Association[v], Dariush Mozaffarian, M.D., Dr.P.H., dean of the Friedman School, said
Placing limits on total fat intake has no basis in science and leads to all sorts of wrong industry and consumer decisions. Modern evidence clearly shows that eating more foods rich in healthful fats like nuts, vegetable oils, and fish have protective effects, particularly for cardiovascular disease. Other fat-rich foods, like whole milk and cheese, appear pretty neutral; while many low-fat foods, like low-fat deli meats, fat-free salad dressing, and baked potato chips, are no better and often even worse than full-fat alternatives. It's the food that matters, not its fat content.
His co-author David Ludwig, M.D., Ph.D., director of the New Balance Foundation Obesity Prevention Center at Boston Children's Hospital, noted the absurd results the guidelines foster. For example, he points out that the National School Lunch program recently banned whole milk while keeping sugar-sweetened non-fat milk on cafeteria menus.
What to do? Stop worrying about fat. Instead, avoid sugar and processed foods that try to manipulate levels of fat, protein, and carbohydrates.
Stick to a whole foods diet with fresh vegetables, fruits, nuts, seeds, full fat dairy, pastured meat and eggs, and wide-caught fish.
[i] Russell J deSouza et al. "Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies." BMJ 2015; 351:h3978 doi: https://dx.doi.org/10.1136/bmj.h3978 (Published 12 August 2015)
[ii] Mozaffarian D, Clarke R. "Quantitative effects on cardiovascular risk factors and coronary heart disease risk of replacing partially hydrogenated vegetable oils with other fats and oils." Eur J Clin Nutr 2009;63:S22-S33.
[iii] Hooper L, Martin N, Abdelhamid A, Davey Smith G. "Reduction in saturated fat intake for cardiovascular disease." Cochrane Database Syst Rev2015;6:CD011737.
[iv] Jakobsen MU, Dethlefsen C, Joensen AM, 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 2010;91:1764-8.