Nutrition advice has moved on from ‘eat low fat’ to ‘incorporate heathy fat as a part of a balanced diet’. But what does this really mean? HFG senior nutritionist Rose Carr finds out.
In the 1980s it was thought we’d be healthier if we followed a low-fat diet because reducing total fat intake means we reduce our intake of saturated fat. Unfortunately, this theory didn’t take into account what we might eat instead! In the US, as food manufacturers took out the fat and added more sugar instead, Americans kept on eating and just got bigger and unhealthier.
For a long time, we also thought we needed to follow a low-fat diet to lose weight and keep it off. And from a mathematical point of view it seemed to make sense. Per gram, fat has around twice the kilojoules of protein or carbs. But fat also offers more satiety than carbs. And let’s not forget that fats add texture and flavour to food; that’s why we love them.
These days, we know it’s more important to think about the types of fats we’re eating, as well as the amounts. And while a lower-fat diet might suit some for weight loss, for others it’s not helpful. So let’s think again about the fats we eat.
Types of dietary fat
The descriptions of fats relate to their chemical structure. First up, they are described as either saturated or unsaturated. Because of their structure saturated fats can pack together tightly, and at room temperature they form a solid fat. Think coconut oil, palm oil and butter.
Unsaturated fats have kinks in their structure so they can’t pack together as tightly, and are liquid at room temperature. Oils such as canola, sesame, olive and rice bran oil are unsaturated fats.
Unsaturated fats can be polyunsaturated or monounsaturated. The polyunsaturated fats are either omega-6 or omega-3 fats. Our bodies can make some fats, but we can’t produce the essential omega-3s and omega-6s, so we must get these from our diet.
The different chemical structures give rise to the names for fats, but we’ve also learned they have different effects on our health.
We need fat
Fats are a critical part of every cell in our body and we need a certain amount of fat in our diet to maintain optimal health. Vitamins A, D, E and K are fat-soluble, so they’re transported in fats. If we don’t eat fats, we won’t get those vitamins. Fats are also a good source of energy; they’re much more energy-dense than protein or carbs. If we need to put on weight, or we’re using more energy for extra activity, it can be easier to up the amount of fat in our diet so the volume of food we eat doesn’t have to increase as much.
The fats that love us back
Plant foods contain mostly unsaturated fats. Olives, avocados, nuts and seeds, and their oils, are all high in healthy unsaturated fats. The exceptions to the ‘plant food’ rule are coconut, palm kernel and palm fats, which are all very high in saturated fats.
Long-chain omega-3 fats (DHA, EPA and DPA) are mainly found in oily fish, so regularly eating fish is the best way to get these fats. The short-chain omega-3 fat (ALA) is found in plant foods such as walnuts, flaxseeds and oil, pumpkin seeds, legumes and canola oil. Higher intakes of the more-studied long-chain omega-3s are beneficial to heart health, and potentially reduce our risk for dementia, diabetes and asthma. Our body’s ability to convert ALA to long-chain omega-3s is fairly limited.
The fats that don’t love us back
Saturated fats, mostly found in animal foods, are associated with atherosclerosis, the beginning of heart and circulatory disease.
This year, the World Health Organization published a review assessing the effect of modifying saturated fat intake on blood lipids by replacing saturated fats with either polyunsaturated fats, monounsaturated fats or carbohydrates. The best effects for total and LDL cholesterol and triglycerides were found when polyunsaturated fat intakes increased as saturated fat intakes decreased.
Many studies have highlighted the link between higher saturated fat intakes and increased risk for cardiovascular disease. Now a study published in August 2016 takes that further, linking higher saturated fat intake with higher death rates from specific causes. The study followed around 125,000 people for over 30 years, finding all-cause mortality increased with higher saturated fat intake and decreased with higher intakes of both polyunsaturated fat and monounsaturated fat.
So the evidence shows less saturated fat and more unsaturated fat, while enjoying a mainly plant-based diet, should see us in good shape.
How to balance our fats
We don’t have to eliminate saturated fat from our diets. But if we’re choosing foods high in saturated fat most of the time, it’s likely we’re getting too much.
Choose these foods for their healthy fats:
- Oily fish: Mackerel, herring, sardines, salmon and tuna all provide long-chain omega-3 fats.
- Nuts and seeds: 25—30g a day (a small handful).
- Avocado: A heart-healthy butter alternative when in season.
- Olive oil: High in monounsaturated fats.
- Nut and seed oils: eg. canola, rice bran, sesame, almond, grapeseed…
Limit these foods:
- Fried foods, pies, pastries, biscuits and cakes: These can all be high in saturated fats.
- Fatty meat: We don’t have to avoid meat, it’s the fat that comes with it we’re limiting.
- Sausages and salami: Reduced-fat versions are available.
- High-fat cheeses: Cheese is good food, but harder cheeses can be especially high in saturated fat, so portion size and frequency are key.
- Butter: A little might not kill you, but it’s best to stick to a small amount, and use alternatives such as avocado.
- Full-fat milk and yoghurts: Choose reduced-fat alternatives instead. The good news is our taste buds adapt quite quickly.
- Cream: Use only when nothing else will do, and preferably a reduced-fat version; otherwise use alternatives such as a Greek-style yoghurt.
- Coconut and coconut fat: Yes, it’s trendy and it’s tasty. And the good news is it’s not as bad for us as butter. But ‘less bad’ does not equal health food wonder. A 2014 Heart Foundation review of the evidence found it is not as good for us as unsaturated plant oils.
- Coconut cream: When you need the flavour, choose a coconut milk with the lowest saturated fat content you can find. For non-HFG recipes, you can reduce the amount and still get the flavour.
What about butter?
Despite attention-grabbing headlines like Time magazine’s ‘Eat Butter’ cover from 2015, butter has not suddenly changed from being a concentrated source of saturated fat we need to be wary of, no matter how ‘natural’ it is. Several studies taken out of context do not change the overwhelming evidence that consuming unsaturated fats instead of saturated fats is better for us. Olive, canola, sunflower, rice bran and other unsaturated oils have all been shown to be better for us than butter. This doesn’t mean we need to banish butter. Remember, it’s the whole diet that counts. With butter, just use it in small amounts, or infrequently.
How much fat do we need to eat?
Here’s an example of an 8700 kilojoule day that meets the recommendations for fat.
2 toast slices grainy bread, topped with sardines (1 can sardines in spring water, drained), 3 tablespoons avocado and sliced tomato
Trim flat white
1 banana, 3 walnuts, 150g pottle low-fat yoghurt
How the day stacks up
Total energy 8650kJ: 35 per cent of kilojoules from fat (the recommendation is for 20—35 per cent of kilojoules)
Saturated fats 14g: 6 per cent of kilojoules (we’re advised to limit saturated fats to 10 per cent or less of our kilojoules)
Monounsaturated fats 42g: 18 per cent of kilojoules
Polyunsaturated fats 25g (omega-6 plus omega-3 fats): 11 per cent of kilojoules
- around 1.3g long-chain omega-3s (the daily suggested dietary targets are 0.61g for men and 0.43g for women)
- at least 1.5g ALA (adequate daily intakes are 1.3g for men and 0.8g for women, but more is better, especially for vegetarians and vegans)