The Why, What and How To of Healthy Fats
Low-fat diets are officially over. Once the key focus to improve chronic disease risk was on eating less fat, in particular saturated fat, to reduce rates of coronary heart disease and obesity; now the focus has shifted to the quality of fats in our diets, rather than simply quantity.
The recently released Australian Dietary Guidelines 419 has shifted its focus to encourage replacing saturated fats with unsaturated fats, with Guideline 3 stating:
Replace high fat foods which contain predominantly saturated fats such as butter, cream, cooking margarine, coconut and palm oil with foods which contain predominantly polyunsaturated and monounsaturated fats such as oils, spreads, nut butters/pastes and avocado.
Including healthy monounsaturated and polyunsaturated fats in the diet, while limiting the amount of saturated fats, has important implications for coronary heart disease, blood lipids, body weight control and even diabetes.
The rates of chronic disease are high: overall, 3% of all Australians have coronary heart disease – it affects 1.4 million of us. The rates rise rapidly as we age, to 7% of people aged 55 to 64, and nearly a quarter of people by 85 420. High blood cholesterol levels are a major risk factor for CHD. More than half of all Australians over the age of 25; 6.4 million people have elevated blood cholesterol 420.
Overweight and diabetes are likewise major concerns. Three in five Australian adults are overweight or obese, 421 and according to the Australian Institute of Health and Welfare, 3.8% of Australians have been diagnosed with type-2 diabetes, that’s nearly 800,000 people in the 2007-8 National Health Survey 422. However, by including healthy unsaturated fats in the diet it’s possible to improve chronic disease risk factors.
Unsaturated fats and heart disease
For many years, the strategy to reduce heart disease risk was based around a low-fat diet, with higher carbs. However, the 20-year results of the Nurses’ Health Study showed that while reducing saturated fats reduced heart disease risk, replacing them with carbs rather than with unsaturated fats offered no heart disease benefits 423. More recently, a major pooled analysis of the effects of reducing saturated fat and replacing it with either unsaturated fats or carbs found that the carbs were no better than the saturated fat in terms of heart disease risk. Unsaturated fats, however, provided protection against heart disease 424.
Oily fish such as sardines, rich in Omega-3 oils, as part of a mediterranean-inspired diet.
The largest randomised controlled trial of a low-fat diet for heart disease prevention is the Women’s Health Initiative Study 425 intended to see how a low-fat diet high in fruits and vegetables (designed to reduce cancer risk) would fare in reducing heart disease. The result? After 8 years, studying nearly 50,000 women, there was no decrease of heart disease or stroke on a low fat diet.
So, a low-fat approach to reducing heart disease is over, replaced now by a strategy to reduce saturated fats while supporting healthy unsaturated fat intake 426.
The recently released results of the PREDIMED Mediterranean Diet study, 427,428 showed that healthy unsaturated fats in a Mediterranean-style diet, not only decreased heart disease risk, 429 but improved inflammatory markers 430,431 and reduced lipoprotein oxidation 432. A meta-analysis looking at the effects of including polyunsaturated fats in the diet, found likewise, that polyunsaturates 433,434.
Unsaturated fats and weight control
Despite what has often been said, a recent study showed that a kilojoule is not just a kilojoule, 435 what really matters is where each kilojoule comes from – fat, protein or carbohydrates. The study, published in the Journal of the American Medical Association, showed that after people had lost weight, the most effective diet for keeping that weight off and at the same time protecting their heart wasn’t a low-fat, high carb diet, it wasn’t a low-carb Atkins-style diet, it was a diet that was similar to the Mediterranean diet – high in plant foods, nuts and legumes, plenty of fish, using lean meats, and focusing on low glycemic index (GI) carbs. More importantly, it was a diet with saturated fat kept low, but with plenty of healthy fats included.
This study isn’t the first to show that including healthy fats in a weight control program has real benefits. Another study 436 which compared this approach to a low-fat diet for weight loss found that after 18 months, people lost more weight on the healthy-fat, Mediterranean-style diet than the low-fat diet. The study also found that the healthy fats made it more enjoyable and easier to stick to.
Unsaturated fats and diabete
A 2011 report of a subset of the PREDIMED study looked at over 400 non-diabetic people and showed that following a Mediterranean diet supplemented with unsaturated fats from olive oil or nuts resulted in 50% reduction in diabetes incidence, compared to the control group 437.
Blood levels of HbA1c are a measure of diabetic control over a three month period. A meta-analysis of the results of nine controlled trials found that diets high in monounsaturated fats were effective in reducing HbA1c and are a useful strategy for treating those with type-2 diabetes by improving their glucose control 438. A recent study reporting on the results of the OmniHeart Trialfound that partially replacing carbs with unsaturated fat can improve insulin sensitivity in people at high risk of heart disease 439.
Avocados tick the healthy fat boxes
Avocados are an excellent source of healthy fats, with a large proportion as monounsaturates and a smaller amount of polyunsaturates. Avocados are also a source of important heart-healthy plant omega-3 polyunsaturated fats (alpha linoleic acid, ALA): a serve of half an avocado (120g) contains 138mg ALA which can contribute to the ~1000mg needed by adults each day.
Including avocado regularly in the diet, as well as other wholefoods which are rich sources of healthy fats such as nuts, seeds and their oils, means healthy fats can do their job in helping to protect heart health. One strategy, in line with the dietary guidelines, is to advise clients to include some healthy fat with every meal: for example, include some avocado as a spread or in a salad, a handful of nuts, a sprinkle of seeds or some olive oil, instead of including saturated fats.
Author: Lisa Yates, Consultant Dietitian Adv APD
Lisa Yates is an Advanced Accredited Practising Dietitian with 16 years experience in nutrition, communications, clinical practice, as well as strategy development and implementation.