If you eat to improve your health, here are five foods to put in your supermarket trolley every week. All pack a proven punch in terms of health gains if you have them regularly.
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Oats are a wholegrain cereal usually eaten for breakfast as porridge or in muesli. They have more soluble fibre than other grains.
A soluble fibre found in the outer endosperm cell wall of this cereal known as beta-glucan reduces absorption of cholesterol in the small intestine. Eating enough oats so you get around three grams of beta-glucan daily reduces your total cholesterol and LDL (bad) cholesterol in both people with high and normal cholesterol.
Half a cup of raw rolled oats (50 grams) contains about two grams of beta-glucan and four grams of fibre. Oat bran is a bit higher with eight to 12 grams of beta-glucan in every 100 grams.
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Put another way, three bowls of porridge a day gives you enough soluble fibre and decreases your total cholesterol so much that if everyone started eating rolled oats, then the incidence of heart disease would drop by about 4 per cent.
Clearly, oats for breakfast are a must. And there's an added bonus – they're cheap, at $4 to $5 a kilogram.
Salmon is an unusual fish because it's so high in fat; at about 13 grams of fat per 100 grams, it has double the fat content of lean steak. But put it on your menu every week anyway because it contains highly specific polyunsaturated fatty acids called omega-3s (1.7 grams per 100 grams fish), which are components of every cell membrane in your body.
Omega-3s, and another group of polyunsaturated fatty acids known as omega-6, get converted into a host of powerful compounds that regulate important body functions, including blood pressure, blood clotting, the brain and nervous system, and the production of molecules that regulate the inflammatory response.
A systematic review of 11 placebo-controlled, double-blind randomised trials, with 15,348 patients who had heart disease, measured the impact of taking one gram of omega-3s daily for at least one year. It found significant protective effects on cardiac death rates, sudden death and heart attacks, even though there was no protective effect for all-cause mortality or stroke.
We need to get the major omega-3 and omega-6 fatty acids from food because our bodies cannot manufacture them. To keep inflammatory processes under control you need a ratio of omega-6 to omega-3 fatty acids of about four to one.
Unfortunately, typical Western diets have a ratio of 15 to one due to use of vegetable oils high in omega-6s. So reduce these and increase the good sources of omega 3s, such as oily fish, soybean and canola oils, flaxseed, walnuts and omega-3 fortified foods, such as eggs.
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We all know that sharing a cuppa is a great way to feel better. A 2013 review published in the American Journal of Clinical Nutrition found drinking tea regularly improves your attention and self-reported alertness, while population studies suggest it's associated with better cognitive function in the elderly.
Tea constituents thought to have neuro-protective effects include L-theanine, caffeine and catechins.
The most powerful data dictating that green and black teas should definitely be in your shopping trolley comes from a Cochrane systematic review of tea and prevention of heart disease. Across 11 randomised controlled trials and a total of 821 healthy adults, including people at high risk of heart disease, drinking black and green teas led to significant reductions in LDL cholesterol and blood pressure.
So, put the kettle on and drink up.
4. Soy foods
A range of health benefits have been attributed to soy foods, although not all the promises hold up to scientific scrutiny.
A review of soy products containing a compound called isoflavones, evaluated the impact of soy protein on heart disease risk. One risk factor is how easily blood flows though your arteries.
In a meta-analysis of 17 randomised trials researchers found a small but significant improvement in blood flow of 0.72 per cent in studies using soy foods, such as soy milk, pasta, soya beans or flour for four to 24 weeks.
The biggest nutritional pay off from eating soy beans or other soy foods regularly is their fibre and protein content. They are low in saturated fat, contain some omega 3s and are a good source of folate, thiamin, riboflavin, iron, zinc and magnesium.
Supermarkets carry a range of soy foods from soy milk, cheese and yoghurt to canned or dried soy beans, tofu, fresh beans, soy "meats" and textured vegetable protein. Experiment until you find the products you like best.
5. A variety of vegetables and fruit
Vegetables and fruit can help ward off type 2 diabetes. A 2012 meta-analysis of five studies involving over 179,000 people found a 7 per cent lower risk ratio of developing type 2 diabetes in those with the highest fruit and vegetable intakes compared to the lowest.
A closer look at specific types of fruit and vegetables, found the relationship was strongest for green leafy vegetables (bok choy, spinach, cabbage, choy sum, all lettuce varieties, rocket, broccoli, silverbeet, watercress). And the longer the studies ran, the stronger the protective relationship.
While a meta-analysis of three studies on fruit intake found that for every three pieces eaten weekly, the hazard ratio for developing type 2 diabetes was 0.98, meaning a small risk reduction.
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Some fruits were better than others. The most protective, in descending order were blueberries, prunes, grapes and raisins, apples and pears, bananas and grapefruit.
Add a vegetable and fruit you have not had for a while to your shopping trolley every week. This variety will boost your fibre, vitamin and mineral intakes. The more colour the better, as it maximises your intake of plant phytonutrients that contribute to good health.
If you fall short of getting 2+5 serves a day, then a target of three fruit and four veg may be easier to start with. Learning to prepare meals that include lots of vegetables or fruit and how to hide them in your favourite recipes will be worth the effort.
Clare Collins is Professor in Nutrition and Dietetics at University of Newcastle. She has received funding from NHMRC, ARC, MLA, HMRI and the University of Newcastle.
This story has been updated since its original publication.