How Much Protein Do You Need to Lose Weight?

If you are eating less to lose fat and you want to keep your muscle, aim for 1.6 to 2.2 grams of protein per kilogram of body weight a day. For an 85kg man that is about 135 to 185 grams. For a 70kg woman, about 110 to 155 grams. That is roughly double the Australian Recommended Dietary Intake, and there is a reason for the gap: the RDI is the amount that stops a healthy adult being deficient, not the amount that protects lean muscle while you are in a calorie deficit and training.

The number you were given is not the number you need

Dietitians Australia puts approximate requirements at 0.75g per kilogram a day for adult women and 0.84g for adult men, rising to about 1g per kilogram for people over 70. For a 70kg woman that is 53 grams a day. It is a reasonable floor for someone whose weight is stable and who is not training hard. It was never designed as a fat-loss target.

This is the most common gap I see on an intake consult. Someone has cut their calories hard, they are training three or four times a week, and they are eating 60 or 70 grams of protein a day. The weight comes off. A chunk of it is muscle. Then the loss stalls, they feel flat, and the body in the mirror looks softer at a lower bodyweight than it did at a higher one.

What to aim for, by bodyweight

• 60kg: about 95 to 130 grams a day
• 70kg: about 110 to 155 grams a day
• 80kg: about 130 to 175 grams a day
• 90kg: about 145 to 200 grams a day
• 100kg: about 160 to 220 grams a day

Use the lower end if you are new to training or finding the volume of food hard to manage, and the upper end if you are in a steep deficit, training hard, or over 50. If you are carrying a lot of excess weight, work off a realistic goal weight rather than your current weight, otherwise the number gets unmanageable.

Where the higher number comes from

The clearest test of this was a randomised trial published in the American Journal of Clinical Nutrition in 2016. Two groups of young men ate a diet with energy cut by about 40 percent for four weeks while doing resistance and interval training. One group ate 1.2g of protein per kilogram a day, the other 2.4g. The higher-protein group gained 1.2kg of lean mass while the lower-protein group gained 0.1kg, and the higher-protein group lost more fat as well: 4.8kg against 3.5kg.

That was young men, four weeks, an aggressive deficit, and all of their food was provided for them. Do not read it as a promise that you will gain 1.2kg of muscle while dieting. What it establishes is the direction: at the same calorie deficit and the same training, protein intake changed what came off.

More is not better past a point

A meta-analysis of 49 randomised trials and 1,863 participants in the British Journal of Sports Medicine found that gains in fat-free mass from resistance training stopped improving once total protein passed about 1.62g per kilogram a day, with a confidence interval running from 1.03 to 2.20. That is the ceiling on the useful range. Going from 1.6 to 2.2 is cheap insurance while you are dieting. Going from 2.2 to 3.0 buys you nothing except a harder day of eating.

Why it gets more important after 40

Better Health Channel notes that from around 50 years of age humans begin to gradually lose skeletal muscle, a process called sarcopenia. The same British Journal of Sports Medicine review found the muscle benefit of extra protein shrank as age went up, and its authors make the point that older people are anabolically resistant: they need a larger dose of protein per meal to get the same muscle-building response a younger person gets from less.

So the older you are, the less margin you have. A 30-year-old who undereats protein for twelve weeks loses a little muscle and rebuilds it quickly. A 52-year-old loses it on top of what age is already taking, and rebuilds it slowly. That is the practical reason we push protein hardest with clients over 45, and it runs through our guides to losing weight after 40 for men and strength training for women over 50.

What that looks like on a plate

Numbers are useless until they become food. Better Health Channel's standard serve sizes are a good reference: 65g of cooked lean red meat, 80g of cooked poultry, two large eggs, 170g of tofu, or 30g of nuts and seeds. A day that lands near 140 grams, without a single supplement, looks like this:

• Breakfast. Three eggs on toast, or 200g of Greek yoghurt with berries. Roughly 20 to 25 grams.
• Lunch. 150g of chicken, tuna or tofu through a salad or a wrap. Roughly 35 to 45 grams.
• Afternoon. 200g of Greek yoghurt, a tin of tuna, or a shake. Roughly 20 to 25 grams.
• Dinner. 200g of steak, fish or chicken, or a solid legume-based meal. Roughly 40 to 50 grams.

Dietitians Australia recommends spreading protein across two to three meals a day rather than loading it into one, because that is better for muscle protein synthesis. In practice the fix for most people is not dinner. It is breakfast and the afternoon. Those two meals are where almost everyone we scan is short, and our nutrition for fat loss guide covers how the rest of the day fits around them.

Four mistakes we see every week

• Counting the meal, not the grams. "I had chicken for lunch" can mean 15 grams or 50. Weigh your protein sources for one week and you will never need to again.
• Treating protein as an add-on. Build the meal around the protein, then add the carbohydrate and the vegetables. Reverse that order and the protein becomes a garnish.
• Drinking the deficit. Alcohol is not only the kilojoules, it also tends to replace a protein-rich dinner with chips at 11pm. We went through the arithmetic in what a big weekend actually costs you.
• Eating the protein and skipping the lifting. Better Health Channel puts it plainly: high-protein diets do not lead to increased muscle mass, it is the stimulation of muscle tissue through exercise that does. Protein is the raw material. Training is the signal. You need both.

Does it have to be powder?

No. Whole food should do most of the work and it will fill you up better. A shake is a convenience tool for the one meal you keep missing, usually mid-afternoon or straight after training. If you can hit your number with food, do that.

One safety note. Dietitians Australia advises speaking to your GP or an Accredited Practising Dietitian before starting a high-protein diet, because very high intakes can add stress to the kidneys. If you have any kidney condition, have that conversation first.

Nine weeks to Christmas, which is exactly the point

It is late October. There are just under nine weeks until Christmas, and work functions start landing from the middle of November. The pattern we see every year is people cutting hard through November to look better at the December events, undereating protein while they do it, and arriving at Christmas lighter on the scale with less muscle than they started with. January then feels harder than it should.

Nine weeks is enough time to lose a real amount of fat. It is also enough time to lose a real amount of muscle, and which one happens is decided largely by your protein intake and whether you are lifting. Protein-first ordering works at a pub too: the steak and the salad, the parmigiana without the chips, the barramundi. You are not being difficult, you are being deliberate. How often you train matters here as well, and we set out the minimum in how many times a week you should train to lose weight.

How we check whether it is working

The scale cannot tell you whether you lost fat or muscle, which is the whole problem with managing a diet by bodyweight. We scan clients on an InBody 570 at the start and then monthly, and the number we watch through a fat-loss phase is skeletal muscle mass. If fat mass is falling and muscle mass is holding, the protein and the training are right. If both are falling, protein goes up and the deficit comes down. Since 2011 we have made that call hundreds of times, and it takes two minutes with a scan and guesswork without one.

If you are dieting right now and you do not know whether the weight coming off is fat or muscle, that is worth finding out before you spend another nine weeks on it.

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