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Question: I want to lose 20 pounds. How do I maintain muscle and lose body fat?

I’m a 40-year-old male who needs to lose 20 pounds. I’ve cut my calorie intake and I am working out five days a week – a mix of cardio and free weights. How much protein do I need to eat to maintain muscle – even gain a little – while I lose body fat?

Answer: To lose body fat and maintain muscle at the same time – and to stay strong – you need to do the right kind of exercise and follow the right kind of diet.

Cutting calories will help you lose weight. But dieting alone can strip away muscle along with body fat. Research suggests that as much as 25 per cent of weight lost by dieters is from muscle. And that's not a good thing.

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Losing muscle while on a calorie-reduced diet can hinder your performance in the gym by reducing strength and stamina. It can also slow your metabolism, so you burn fewer calories during the day, making it harder to lose weight – and easier to gain it back.

The amount of muscle you have is the biggest contributor to your resting metabolism – the number of calories the body burns to carry out basic functions such as breathing, keeping your heart beating and growing and repairing cells. Muscle burns more calories than fat, so the more you have, the higher your metabolic rate.

How to maintain muscle while losing weight

Two key strategies will help preserve muscle while dieting: resistance exercise and eating extra protein at the right times. Doing both may even help you put on extra muscle as you shed pounds.

Numerous studies have demonstrated the ability of resistance exercise to protect against the muscle loss that typically occurs with dieting. (Resistance exercise is any type of exercise that forces your skeletal muscles to contract, such as free weights, weight machines, resistance bands and whole body exercises.)

A small 2014 study conducted by Australian researchers found that after five days on a low-calorie diet, muscle protein synthesis declined by 27 per cent in healthy young men and women. Resistance training, however, restored the rate of muscle protein synthesis, the process by which muscles grow.

Enter protein. More of it – considerably more than the official recommended daily intake (RDA) – can boost the muscle-sparing effects of resistance training.

The RDA for protein, which was not designed for heavy exercisers or athletes, is 0.8 grams per kilogram of body weight. For an 88-kg (195-pound) male, that translates into 70 g of protein a day, an amount you'd get by eating two eggs, one cup of Greek yogurt and five ounces of salmon.

A U.S. study published in 2013 revealed that among volunteers who followed a calorie-restricted diet and exercised, those who consumed two and three times the RDA for protein had less muscle loss and greater fat loss compared with those whose protein intakes matched the RDA. (Interestingly, consuming protein at levels beyond twice the RDA did not offer greater protection against muscle loss.)

Eating more protein can help put on muscle, too. Protein supplies amino acids, the building blocks muscles use to create muscle tissue, and enhances muscle protein synthesis.

A 2012 review of 22 randomized controlled trials concluded that supplementing a normal diet with protein powder immediately before, during or after resistance training increased muscle mass and strength in younger and older adults who weren't restricting calories.

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Is it possible to build muscle, though, if you are dieting to lose weight? According to researchers from McMaster University in Hamilton, the answer is yes.

A four-week study, published in 2016 in the American Journal of Clinical Nutrition, fed 40 overweight young men a diet providing 2,300 calories a day, 40 per cent fewer than their usual diet.

Half of them were assigned to consume a lower protein diet – 1.2 g per kg per day, an amount already higher than the RDA; the others received more protein – 2.4 g/kg/day. All were given whey protein drinks to consume during the day, including one immediately after exercise.

All the men completed strenuous resistance training combined with high-intensity interval training six days a week.

Both groups lost a substantial amount of weight. Those who followed the lower protein diet didn't lose any muscle during the four weeks. But the men who ate the higher-protein diet increased lean muscle by almost three pounds. They also lost more body fat.

Keep in mind this study was small – just 20 men assigned to each diet – and of short duration. The calorie restriction (40 per cent) was extreme, and the exercise regimen was intense.

No doubt it helped that the participants were provided all their meals and beverages during the study. Whether such a regimen is sustainable in the long term in free-living conditions seems highly unlikely.

Even so, these findings, taken together with those from previous studies, point to the important role of resistance training and protein in preserving muscle during weight loss. Their synergistic effect can counteract unwanted muscle loss and, perhaps, even augment muscle.

The optimal daily dose of protein for gaining muscle while shedding body fat isn't clear, nor is it for preserving muscle. What does seem evident though, is that as long as you're exercising, it requires more than the official RDA.

According to Dr. Stuart Phillips, a professor and Canada research chair at McMaster University and senior author of the McMaster study, you'll be in good shape if you aim to get two grams of protein for every kilogram you weigh.

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If your weight-loss regimen includes resistance training and a calorie-reduced diet, consider these four strategies to help you add muscle while losing weight.Anchiy/iStockPhoto / Getty Images

Four tips to maintain – and build – muscle while losing weight

If your weight-loss regimen includes resistance training and a calorie-reduced diet, the following strategies will help you hang on to – or gain – muscle while you shed pounds.

Get enough protein

To maintain lean muscle, consume at least 1.2 g of protein per kilogram of body weight each day with foods such as lean meat, poultry, fish, eggs, yogurt, milk, soy beverages, tofu and legumes.

To gain muscle while losing fat, aim for 2 to 2.4 g of protein per kilogram of body weight. For a male who weighs 88 kg (195 pounds), that means 176 g of protein each day. To hit that target, you'd need to eat four egg whites, 14 ounces of lean meat, poultry or fish, two cups of milk, plus protein supplements.

Spread it out

Include protein at all meals and snacks to give your muscles a constant supply of amino acids for growth. If you typically eat most of your protein at dinner, shift some to breakfast and lunch.

Forget low carb

If you don’t eat enough carbohydrates – e.g., whole grains, fruit, starchy vegetables – you’ll sacrifice muscle as you lose weight. And you’ll feel weaker, too.

Carbohydrates fuel your muscles to do the work (e.g., resistance training) that stimulates them to get bigger. Without enough carbs, the extra protein you eat will be used for energy instead of muscle repair and growth.

Include a source of carbohydrate at all meals and snacks.

Supplement with protein powder

Drink a protein shake immediately after resistance training to supply primed muscles with the amino acids needed for repair and growth. Research suggests that consuming 30 g of protein (instead of 15 g) after a workout is more effective at stimulating muscle protein-building.

Blend protein powder with milk or non-dairy milk and fruit (e.g., banana, berries) to get muscle-glycogen replenishing carbohydrates.

For some people, using protein supplements helps meet the higher protein requirements needed to gain muscle without going over allowable calories.

Leslie Beck is a dietitian. Follow her on Twitter @LeslieBeckRD.