Your weight and your shape follow different rules

Eat fewer calories than you burn and your weight goes down, and eat more and it goes up. That holds on any diet.

The NSCA, a major strength and conditioning group, finds no best diet for fat loss.² Low-carb and low-fat diets work equally well when calories fall below maintenance, and the total calories eaten and the ability to stay on the diet made the biggest difference. It recommends a moderate deficit, which means eating about 500 calories less than you burn each day.

A large trial agrees. In a 2018 study of 609 adults, a low-fat group lost 5.3 kg in 12 months and a low-carb group lost 6.0 kg, a gap small enough to be chance.³

Not every expert agrees. Cate Shanahan, a physician and the author of Deep Nutrition, argues that what's in your food matters as much as its calories.⁴ The trials lean toward the calorie view, but her dissent is worth knowing about.

Bottom line

Weight is simple. Eat less than you burn and you lose weight, period.

A calorie of candy counts the same as a calorie of broccoli, but the difference is how much you end up eating, because processed food doesn't keep you full as long.

A 2019 study from the US National Institutes of Health tested this.⁵ Twenty adults lived in a hospital unit for two stretches of 14 days. They ate ultra-processed meals for one stretch and unprocessed meals for the other, with the meals matched on presented calories, sugar, salt, fiber and nutrients, and people could eat as much as they wanted.

On the processed meals, people ate about 508 more calories a day and gained 0.9 kg. On the unprocessed meals, they ate less and lost 0.9 kg.

It was a small, short study, so it shows the direction of the effect and not its size over years. The authors don't say why people ate more.

Bottom line

Think about how hungry you'd be after a huge bowl of green vegetables compared with a can of soda. A can of soda has about 140 calories, and a bowl of vegetables with the same calories is enormous. Only the vegetables keep you full until your next meal, so you don't grab a snack in between.

Your shape depends on how much muscle you carry and how much fat covers it. Lifting is the main way to build muscle, and protein is the second.

In a 2016 trial, 40 young men ate about 40 percent fewer calories than they needed and trained six days a week.⁶ Half ate 2.4 grams of protein per kilogram of body weight. Half ate 1.2 grams.

Both groups cut calories hard. Only the protein changed.

A review of 49 trials with 1,863 people found protein supplements added about 0.3 kg of muscle on top of weight training.⁷ Gains stopped growing at about 1.6 grams per kilogram a day. For a 180 lb person, that's roughly 130 grams.

The effects were small but pointed the same way, and most studies were short and in younger people, with a benefit that shrank with age.

Bottom line

Lift to build muscle and eat enough protein to feed it. Together they help decide how much of your weight loss is fat.

A run doesn't cancel out a meal, because it's easier to skip 300 calories than to burn them off.

Here is what 300 calories looks like. A 180 lb person burns roughly 130 calories per mile of running, counting only the extra above what they'd burn sitting still. So 300 calories takes about 2.3 miles, or around 23 minutes at a 10-minute mile. The same 300 calories is about two and a half glasses of wine, two cans of soda, or a medium order of fries.

A review of exercise and weight loss found that clinically significant weight loss is unlikely unless you do a very large amount of cardio.⁸ People who followed standard public health advice lost about 2 kg, with wide differences between individuals.

Cardio is still worth doing, because Attia calls exercise the most powerful longevity drug¹ and the same review says activity helps your health even when your weight stays put.

Bottom line

Cardio is for your heart and blood sugar. If you want your weight to move, change what you eat.

"Toned" isn't a kind of muscle. You have muscle, and you have fat on top of it. Lighter weights with more reps build muscle about as well as heavier weights with fewer, so neither gives you a different shape.

A 2017 review pooled 21 studies that compared light and heavy weights, with every set taken until the lifter couldn't do another rep.⁹ Muscle growth was about the same. Strength rose more with heavy weights.

Those studies can't tell us whether stopping short of failure works as well. What they do show is that failure at a heavy weight, around rep 6, and failure at a light weight, around rep 30, grow muscle about equally.

Bottom line

Hard sets that end at failure build muscle, whether that's on rep 6 or rep 30. So why do the extra work? Heavier sets take fewer reps and leave you stronger.

The fat you eat and the fat on your body are different things, and cutting fat from your meals doesn't remove body fat unless your total calories drop too.

In a 2015 hospital-ward trial, 19 adults with obesity ate two diets with the same calories for 6 days each, one low in fat and one low in carbs.¹⁰ The low-fat diet lost 89 grams of body fat a day and the low-carb diet lost 53. That edge went to low-fat, but it was small and it lasted only six days. In the 12-month trial above, the two diets came out about even.³

What matters is the calorie count, and fat packs more of it. A gram of fat has about 9 calories, while a gram of carbohydrate has about 4.² A tablespoon of butter is only about 14 grams, yet it holds roughly 100 calories. Watch calorie-dense fats like butter and oil, because a small amount adds up fast.

Bottom line

Your body fat follows the calorie math, not the fat label. Count the calories, and remember that fat is the densest of them.

1. 01

   Weight is calories in against calories out, on any diet.

2. 02

   Filling food helps you eat less, and processed food does the opposite.

3. 03

   Lifting and protein shape how you look.

4. 04

   Cardio is for your health, and it burns fewer calories than a snack adds.

5. 05

   Hard sets build muscle at any rep count, so pick the heavier ones.

6. 06

   Body fat follows total calories, and fat is the densest source.