Your calories, pace and protein

Eat about 500 to 1,000 calories a day below your maintenance, which loses 1 to 2 pounds a week for most people, and slow down as you get leaner. Eat 1.2 to 1.6 g of protein per kg of your body weight every day. Under that is too low.

Why do calorie numbers feel so random?

Most people start with a number they found somewhere. It might be 1,200 calories, because a friend used it, or whatever an app printed after asking their height and weight. Then they treat it as exact, and when the scale doesn’t move in a week they decide calories don’t work for them.

A calculator works more like guessing someone’s salary from their job title. It’s close for most people and off by a few hundred for some. Your scale is your bank statement. After a few weeks it shows what you really earn, and that’s the number to plan with.

The best of the formulas, Mifflin-St Jeor, was built in 1990 from measurements of 498 healthy adults. A 2005 review of the formulas found it came within 10% of the measured number for more people than any other, and also found real errors when it’s applied to one person. On a maintenance of 2,400 calories, 10% is 240 calories a day, about half of a typical deficit.

How many calories should you eat?

1. Find your maintenance. That’s how much you eat to stay the same weight. Use the maintenance calculator, which runs the formula above with your activity.
2. Take off your deficit. A pound of bodyfat holds about 3,500 calories, so each pound a week is about 500 calories a day. For 1 to 2 pounds a week that’s 500 to 1,000 calories under maintenance. The calories to lose calculator does it for your weight and pace.
3. Hold it for three or four weeks. The first week mostly shows water, so don’t judge it.
4. Correct it from your trend. If you’re losing slower than planned, take off another 100 to 200 calories. If faster, add some back.
5. Re-check every 10 to 15 pounds. Each pound you lose lowers the calories you need by roughly 10 a day, so 15 pounds is about 150 calories off your maintenance.

Don’t go below the floor. The 2013 US obesity guideline suggests 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men, or a deficit of 500 to 750 a day. We wouldn’t go under the low end of those ranges without a doctor, because below them it gets hard to eat enough protein and stay full.

The formula, for the curious

Mifflin-St Jeor estimates the calories you burn at rest. Men: 10 × weight in kg, plus 6.25 × height in cm, minus 5 × age, plus 5. Women: the same, minus 161 instead of plus 5. A calculator then multiplies that by your activity to get your maintenance.

For a 40 year old woman who is 5 foot 5 (165 cm) and 180 pounds (81.6 kg), the resting number is about 1,486 calories. Her maintenance with some activity lands somewhere near 2,000, and her scale decides the rest.

How fast should you lose weight?

Moderate The evidence that going slower keeps more muscle comes mostly from small trials in lean athletes. Weak Whether slower loss keeps more weight off for years is less clear.

The CDC says people who lose weight at about 1 to 2 pounds a week are more likely to keep it off than people who lose it faster. We’d put it as a share of your weight, about 0.5 to 1 percent a week, because 2 pounds a week is a different thing at 300 pounds than at 140.

The 2013 guideline suggests a deficit of 500 to 750 calories a day, and the NIH heart and lung institute’s older practical guide says 500 to 1,000 a day gives 1 to 2 pounds a week. We’d stay at or under 1,000 a day, even at 260 pounds.

The heavier you start, the more of a fast loss is fat. That’s why a person at 35% bodyfat can run at 1% a week, and a person at 15% is better off near 0.5%.

How long will it take?

Divide the pounds you want to lose by your weekly pace, then add about a fifth, because the loss slows as you get lighter. At 1.5 pounds a week, 20 pounds takes about 13 weeks on paper and closer to 16 in real life. The calories to lose calculator gives you the date.

For a long diet, plan breaks at maintenance on the way. The NIH’s heart and lung institute suggests a first goal of losing 5 to 10 percent of your weight over about six months. How long to diet before a break covers when to stop and hold.

How much protein do you need?

Most people losing fat do well on 1.2 to 1.6 g of protein per kg of body weight a day, the range in the 2025 to 2030 US Dietary Guidelines. Under it is too low, and many people are, more so with age: in a US survey of 11,680 adults over 50, up to 46% of the oldest ate less than even the old minimum. The Gyroscope app personalizes yours. These ranges are there to show you if you’re too low, and the protein calculator and your personalized guide work them out for you.

If you have more than a fifth of your weight to lose, count from a weight nearer your goal: your goal plus a fifth of what you weigh now. That’s why the last row isn’t counted from 260. Fat tissue doesn’t need protein, so a rule on total weight alone gives a 300 pound person more than their muscle can use.

Protein does two jobs on a diet. It protects muscle, and it fills you up. In a 2005 trial, 19 adults who moved from 15% to 30% of their calories as protein ate about 441 fewer calories a day without being asked to, and lost about 11 pounds (4.9 kg) in 12 weeks.

What the research says about how much

If you lift hard and you’re already lean, going above the typical range can help. In a 2016 trial, 40 young men ate 40% under their needs for four weeks and trained hard. The group on 2.4 g per kg of bodyweight gained about 2.6 pounds (1.2 kg) of lean mass and lost 10.6 pounds (4.8 kg) of fat. The group on 1.2 g held their lean mass and lost 7.7 pounds (3.5 kg) of fat.

If your weight is normal but your waist isn’t

Some people have a normal weight on the scale and a soft middle, often called skinny fat. A diet on its own would take some muscle with the fat. We’d start by lifting at least two days a week and eating your protein at your usual calories for two or three months. Your weight may barely move while your waist comes in. Then decide whether to cut.

The NIH’s heart and lung institute sets the waist lines at over 40 inches for men and over 35 for women.