Protein supplements are often targeted at active people – everyone from weekend warriors and gym junkies to elite athletes. While it's true that athletes have higher protein needs than less active people, it's debatable whether they really need a supplement.

Muscle growth and repair

Working your muscles hard breaks them down, and when you rest and recover, your body gets to work rebuilding them. To do this, it uses amino acids, the building blocks that make up protein.

The recommended amount of protein per day for athletes ranges from 1.2–2.0 grams per kilogram of body weight.

How much and when?

After working out, muscles are receptive to making use of protein, so eating protein shortly after training gives the maximum benefit. The optimal amount of protein for a post-workout snack is thought to be about 20–30 grams.

There's much debate about how long this muscle-synthesis window of opportunity is – some experts say it's as little as 30 minutes, but it's likely 1–4 hours. Muscle repair and growth continues over 24 hours, so you can continue to reap the benefits from subsequent meals.

Whey to go

Whey protein found in milk is considered an ideal protein choice because it's high in the key muscle-building amino acid called leucine, and is digested quickly, so it's available when the body's ability to make muscle tissue is at its peak. It's also cheap and readily available as a waste product in the cheese-making process. Vegan supplements, made from soy, pea and/or rice protein, are increasingly popular.

Real food's good too

Protein supplements aimed at recovery should contain a mix of protein and carbohydrates, and can be a convenient option, especially if you're travelling or your next meal is a long way off. But milk, yoghurt, smoothies and breakfast cereal with milk are also recommended.

Maybe skip the low-carb post-workout?

When you work out, your body uses glycogen, a glucose-based form of energy stored in muscles and the liver. Having some sugar, honey, maple syrup or other simple carbohydrates after exercise helps restore glycogen. Simple carbs also cause an increase in insulin levels in the blood, which increases the uptake of amino acids and further boosts muscle growth. So consider having these products, rather than 'low-carb' alternatives.

Added extras

Supplements aimed at bodybuilders and sports people sometimes contain added extras like certain vitamins and minerals, as well as creatine and legal stimulants such as caffeine. But they may also contain unexpected – and undisclosed – ingredients such as prohibited stimulants, steroids, diuretics and heavy metals.

Bottom line

People who exercise heavily tend to have a greater appetite, and they usually get enough protein from normal food without the need for a special high-protein diet or supplements.

That said, for serious athletes it might be convenient to have commercial protein supplements like drink powders and bars on hand post-workout. Supplements can also help ensure athletes who are reducing food intake to meet weight requirements get enough protein.

Another major target market for protein supplements is people trying to lose weight. Visit a pharmacy, health food store or supermarket and you'll find a huge range of protein powders, bars and snacks claiming to help with weight loss.

And it's true – protein can help.

• Protein helps keep you feeling fuller for longer.
• Kilojoule for kilojoule, it requires more energy than fat or carbohydrates to process and store in the body.
• Having adequate protein when decreasing kilojoule intake also helps reduce the loss of muscle tissue, especially when combined with resistance training.

Weight-loss protein supplements are low-carb and sweetened with intense sweeteners such as stevia or sucralose.

Supplements as meal replacements

Some protein supplements designed for weight loss contain added vitamins and minerals and can be used as a meal replacement. If this is what you're looking for, check the label – it should say whether it's suitable as a meal replacement, or if it's merely a supplementary drink or snack.

Fat-burning ingredients

If you're looking for that extra weight-loss edge, will fat-burning or thermogenic ingredients help? Unfortunately it seems that so-called thermogenic ingredients (those that tend to increase heat in the body) such as L-carnitine, green tea extract or caffeine, won't do much for weight loss above and beyond exercise and sensible eating.

But do you really need special supplements?

Most Australians get plenty of protein in their diet and don't need protein supplements to achieve weight loss. A diet featuring vegetables, fruit, whole grains, low-fat dairy and lean protein is consistently linked with successful weight control. Try replacing high-sugar or high-fat manufactured snack foods with whole foods such as plain yoghurt, a handful of nuts and seeds or a hard-boiled egg.

Nutrient needs in adults change with age, and it's increasingly recognised that elderly – and also possibly middle-aged – people need more protein than younger adults. Because of changes in your metabolism, you need a larger 'dose' of protein to stimulate the muscle-building process. Inadequate protein is linked with loss of bone mass (osteopenia and osteoporosis) and muscle wastage (sarcopenia), and also affects immunity and wound healing.

How much do middle-aged and older adults need?

The Nutrient Reference Values for Australia and New Zealand recommend 0.75g/kg for adult women and 0.84g/kg for adult men. At 70, however, this increases to around 1 gram (1.07 grams per kilogram for men and 0.94g per kilogram for women).

But it's likely the optimal protein intake for adults over 50 may be higher than the current recommendations, with research suggesting that levels of 1–1.3g/kg would meet the protein needs of middle-aged and older adults while avoiding issues of too much protein, such as kidney and liver problems, and loss of calcium.

However, just as protein needs of older adults increase, the amount of food eaten tends to decrease: less physical activity and changes in taste and smell reduce appetite, food may be harder to chew and swallow, and cooking habits may also change, especially for those living alone. Unless a conscious effort is made to ensure there's adequate protein, people may not get enough to meet their needs.

Marketers have cottoned on to this, and are promoting protein powders as a way for older people to ensure they're getting enough.

Added nutrients, added complexity

Some added nutrients may interfere with medications commonly taken by older people. Potassium, for example, interferes with ACE inhibitors (taken for blood pressure and heart failure), while vitamin K interferes with warfarin (a blood thinner). Other nutrients including iron, calcium and magnesium may interfere with certain antibiotics, thyroid medication, osteoporosis medication and/or other drugs if taken at the same time, so the advice is to take them several hours apart.

It's important to talk to your doctor when taking any supplements in addition to prescription medication.

Healthy ageing and sarcopenia

Sarcopenia is the loss of the amount and strength of muscle as we age. Starting from middle age, it accelerates at around 70 years of age.

Loss of muscle strength can impact heavily on quality of life, affecting mobility, increasing the risk of falls and fractures and making it difficult to perform daily activities – dressing, personal care, household tasks, shopping and so on. It's also linked with diabetes, because muscle plays an important role in blood glucose regulation.

However, it isn't inevitable and it is reversible – a program of strength training combined with adequate protein means you can successfully maintain and rebuild muscle mass.

Bottom line for 50-plus

Taking protein supplements isn't as effective as eating whole foods high in protein because there are other nutritional benefits in whole foods that you don't get from protein alone. Most people get enough protein from a balanced diet.

However, for some people – especially frail elderly people who have little interest in eating – supplements could be the best option. Your doctor can give you a referral to a dietitian, and you may be eligible for a Medicare rebate.

While vegetarians are well-served by eggs and dairy protein, which contain essential amino acids, vegans rely on protein from plant sources – soy products, legumes, nuts, seeds and grains. It's perfectly possible to get enough protein from a well-planned plant-based diet, but some vegans find protein supplements an easy and convenient way to get a decent protein hit containing all the essential amino acids.

They may be particularly useful for athletes needing larger than usual amounts of protein, people just starting out on their vegan adventure who haven't got the 'well-planned' aspect of diet down pat, and people on the go who don't get a lot of choice about what they're eating throughout the day.

Vegan protein supplements are often made from soy, which contains all the essential amino acids, or pea and rice protein which together contain good amounts of the essential amino acids.