What to Eat to Lose Fat or Build Muscle: Protein, Carbs and Kilojoules

Written by Robbie Clark, BExSc (Nutrition), M (Nutr+Diet), Accredited Practising Dietitian (APD) and Exercise Scientist · Last updated 19 October 2026 · 8 references

Whether you want to lose body fat or build muscle, what you eat can make a big difference to your results. The two goals need opposite energy intakes, but they have one thing in common: protein. Here's how to eat for each.

What should you eat to lose fat?

To lose fat, you need to take in a little less energy than your body uses. But how you create that gap matters for how you feel and what you lose.

Protein is the most helpful nutrient here. In studies of people eating less to lose weight, higher-protein diets led to more fat loss and helped people keep more of their muscle than lower-protein diets. Protein also helps you feel fuller after a meal. The benefits come from eating about 1.2–1.6 g of protein per kg of body weight a day, with at least 25–30 g at each meal.¹

Good sources of protein include:⁶

• Fish, especially oily fish like salmon and sardines
• Lean meats such as chicken, turkey, pork, beef and kangaroo
• Eggs
• Natural or Greek yoghurt, milk and cheese
• Legumes, tofu and tempeh
• Nuts and seeds

Build the rest of your plate around vegetables, fruit and wholegrains. They're filling for the kilojoules they provide and give you the fibre and nutrients you need while eating less.

Do you need to cut carbs to lose fat?

No. You may have heard that carbs raise insulin, insulin stores fat, and so cutting carbs burns more fat. The research doesn't support this.

In a tightly controlled trial, adults with obesity spent time on two diets that cut the same number of kilojoules, one by cutting carbohydrate and one by cutting fat. Cutting carbs lowered insulin, but people lost less body fat than when they cut fat.² And in a year-long trial of more than 600 adults, a healthy low-carb diet and a healthy low-fat diet led to similar weight loss (about 6 kg and 5 kg).³

The best approach is the one you can stick to. If you prefer fewer carbs, that's fine, but choose high-fibre carbohydrates rather than cutting them out, especially if you train hard.

What should you eat to build muscle?

To build muscle, you need to eat a little more energy than you use, alongside regular resistance training. A review of nutrition for muscle gain recommends eating about 10–20% more than your maintenance needs (for many people, roughly 1,250–2,100 kJ extra a day) and aiming to gain about 0.25–0.5% of your body weight a week. For an 80 kg person, that's about 0.2–0.4 kg a week.⁴ Gaining faster than this tends to add more fat than muscle. Check your progress every few weeks and adjust, as your needs change over time.

Carbohydrate fuels the training that drives muscle growth, so don't skimp on it. Good choices include oats, brown rice, wholegrain and seeded breads, quinoa, potatoes, legumes and fruit. Add healthy fats from olive oil, avocado, nuts and seeds.

If eating more feels like a struggle, spreading your food across 3–6 meals and snacks a day can make it easier.⁴ Choose foods that are nutritious as well as energy-dense, like nuts, nut butters, milk, yoghurt and dried fruit.

How much protein do you need to build muscle?

A review of 49 trials found that eating extra protein while doing resistance training helped people gain more muscle and strength. The benefit levelled off at about 1.6 g of protein per kg of body weight a day; eating more than that didn't add more muscle on average.⁵ Some people, such as experienced lifters, may benefit from up to 2.2 g per kg.⁴

For an 80 kg person, 1.6 g per kg is about 130 g of protein a day. Spread it across your meals and snacks, about 0.4–0.55 g per kg at each meal, or roughly 30–45 g for that 80 kg person.⁴

Do you need protein powder?

No, but it can help. Most people can meet their protein needs from food. Protein powders and drinks are a convenient option if you're busy, have a small appetite, or find it hard to reach your target from meals alone.⁷ In the review of 49 trials, extra protein helped most in people whose total intake was below about 1.6 g per kg.⁵ If you already eat enough protein from food, powder is unlikely to add more muscle.

Frequently asked questions

Can you lose fat and build muscle at the same time?

It's possible, especially if you're new to training, but most people get better results by focusing on one goal at a time. Eating enough protein while losing weight helps you keep the muscle you have.¹

How much protein do I need a day to lose fat?

About 1.2–1.6 g per kg of body weight a day, with at least 25–30 g at each meal.¹

How much protein do I need to build muscle?

About 1.6 g per kg of body weight a day for most people, alongside resistance training.⁵

Is low-carb better for fat loss?

Not on its own. Over 12 months, low-carb and low-fat diets led to similar weight loss.³

How many extra kilojoules do I need to build muscle?

About 10–20% more than your maintenance needs, aiming to gain about 0.25–0.5% of your body weight a week.⁴

References

Research (PubMed)

1. Leidy HJ, Clifton PM, Astrup A, et al. The role of protein in weight loss and maintenance. Am J Clin Nutr. 2015;101(6):1320S–1329S. PubMed 25926512
2. Hall KD, Bemis T, Brychta R, et al. Calorie for calorie, dietary fat restriction results in more body fat loss than carbohydrate restriction in people with obesity. Cell Metab. 2015;22(3):427–436. PubMed 26278052
3. Gardner CD, Trepanowski JF, Del Gobbo LC, et al. Effect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: the DIETFITS randomized clinical trial. JAMA. 2018;319(7):667–679. PubMed 29466592
4. Iraki J, Fitschen P, Espinar S, Helms E. Nutrition recommendations for bodybuilders in the off-season: a narrative review. Sports (Basel). 2019;7(7):154. PubMed 31247944
5. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376–384. PubMed 28698222

Australian guidelines

6. NHMRC. Eat for Health: lean meats and poultry, fish, eggs, tofu, nuts and seeds and legumes/beans. View source
7. Sports Dietitians Australia. Protein supplementation fact sheet. View source
8. healthdirect. Butterfly Foundation. View source

This article is general information, not medical advice. Your needs are individual – speak with your practitioner about the right approach for you.