Bulking and cutting: are you gaining muscle or fat?

When you bulk, the scale goes up. The only question that matters is how much of that is muscle and how much is fat. A weighing machine cannot tell you. A body composition scale can, if you read skeletal muscle mass and body fat mass together, once a month, under the same conditions.

The same goes for cutting in reverse: you want the fat to come off while the muscle stays. This guide covers sensible rates for both phases, how to read the monthly numbers, and what to change when they go the wrong way.

What bulking and cutting are for

A bulk is a period of eating a little more than you burn, so your body has spare energy to build muscle while you train hard. A cut is the opposite: a period of eating a little less, to lose the fat that came along with the muscle, while training hard enough to keep what you built.

The idea is sound. The trouble is that both phases are judged by the wrong number. A good bulk and a bad bulk can show the same weight gain. A good cut and a muscle-wasting one can show the same weight loss. The difference is in what the kilos are made of.

If you are new to lifting or carrying a fair amount of fat, you may not need separate phases at all. Many people in that position can lose fat and gain muscle at the same time; our guide to body recomposition explains when that works.

How fast to bulk, and how fast to cut

Bulking

Muscle is built slowly, even in good conditions. Eat far more than you need and the extra mostly becomes fat. A 2019 narrative review in the journal Sports suggested a modest calorie surplus with a target gain of around 0.25 to 0.5 percent of body weight a week for novice and intermediate bodybuilders, and slower for advanced lifters. For a 70 kg lifter, that is roughly 175 to 350 grams a week.

Protein matters too. The same review suggested 1.6 to 2.2 grams per kilo of body weight a day during a bulk, which sits within the range the International Society of Sports Nutrition recommends for people who train. Spread it over three or four meals.

Cutting

Lose weight too quickly and more of it tends to come from muscle. A 2014 review of contest preparation in the Journal of the International Society of Sports Nutrition recommended losing about 0.5 to 1 percent of body weight a week to help retain muscle, with a high protein intake and continued heavy training. For a 75 kg lifter, that is roughly 375 to 750 grams a week.

Keep lifting heavy during a cut. The training is the signal that tells your body the muscle is still needed. Cutting the weights along with the calories is one of the most common reasons people lose muscle in this phase.

Reading the scale during a bulk

Compare each monthly check with the start of the phase. You are looking at two numbers side by side: how much skeletal muscle mass changed, and how much body fat mass changed.

One honest caveat: body composition scales read water, and lean tissue is mostly water. A big change in carbohydrate intake, salt, hydration or a hard leg session the day before can nudge the muscle reading up or down. That is why you test in the same state each time and trust trends over single readings.

Reading the scale during a cut

In a cut, success looks like body fat mass falling steadily while skeletal muscle mass holds roughly flat. A small dip in the muscle reading in the first week or two is common, as stored carbohydrate and the water that comes with it drop away. A steady slide month after month is a different story: it usually means the deficit is too steep, protein is too low, or training has eased off.

If you want to understand why the scale shows both lean body mass and skeletal muscle mass, read our guide to lean body mass vs skeletal muscle mass.

What Dial H40 adds for people who train

All three InBody Dials measure each arm, each leg and the trunk separately, using 8 electrodes at your hands and feet. Dial H40 is the one built for training. It gives 14 readings, measures at three frequencies in about 20 seconds, and adds two things the others do not have.

• Leg muscle level. A level for the muscle in your legs, useful when squats and deadlifts are a big part of your programme.
• Three balance ratings. Upper-body, lower-body and upper–lower, each shown as Balanced, Slightly unbalanced or Extremely unbalanced. It is a rating, not kilos per limb.

If you train at home with family, Dial H30 recognises up to 20 people and includes the upper–lower balance rating. If it is just you and you mainly want the core numbers, Dial H20 shows skeletal muscle mass, body fat mass and visceral fat level over Bluetooth.

Dial H40For people who train. 14 readings, leg muscle level and three balance ratings, in Beige or Black.See Dial H40 →

Clean readings when you train hard

1. Test on rest-day mornings. After the toilet, before food and training. Hard sessions move water around for hours.
2. Keep food and salt steady the day before. A big refeed or a salty restaurant meal can shift the next morning’s readings.
3. Average two or three mornings. Use the weekly average as your monthly check-in number.
4. Change one thing at a time. Adjust calories or training, then give it four weeks before judging.

Our guide to consistent readings has more on routine. For Dial H20, a 2023 study in the British Journal of Nutrition found it tracked body composition change over 12 to 16 weeks.

Questions people ask