Body Composition Planner: Fat Loss, Muscle Gain and Recomposition

Should you cut, bulk or try to do both at once? This planner estimates your maintenance calories and then shows, for your body weight, what research has actually compared: slow versus fast weight loss, small versus large calorie surpluses, and the protein intakes linked with keeping or gaining muscle. It shows the evidence and my own experience, not a diet prescription.

How the estimate works

Resting energy expenditure is estimated with the Mifflin–St Jeor equation (men: 10 × weight + 6.25 × height − 5 × age + 5; women: same − 161); this planner then multiplies it by an estimated activity factor to approximate maintenance calories.¹ In a systematic review, the Mifflin–St Jeor equation predicted resting metabolic rate within 10% of measured values in more people than other equations, but not in everyone,² so the planner shows a ±10% range and the real-world weight trend should guide any adjustment.

Why the scale can mislead

During recomposition, fat loss and muscle gain can cancel out on the scale.^13,14 In one trial, a high-protein group lost 1.7 kg of fat while body weight changed by only −0.1 kg.¹³ Muscle does not weigh more than fat kilogram for kilogram, but it is denser, so the body can look and measure differently at the same weight.¹⁴

References

Every figure and statement in this tool is linked to a source: the original study where my article cites one, otherwise my own article on the topic. The small numbers in the text refer to this list.

1. Mifflin et al. 1990. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr.
2. Frankenfield et al. 2005. Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults: A Systematic Review. Journal of the American Dietetic Association.
3. Slow versus fast weight loss in elite athletes
4. Dr. Antti Rintanen: Is Bulking Necessary for Muscle Gain?
5. Anyiam et al. 2024. A Systematic Review and Meta-Analysis of the Effect of Caloric Restriction on Skeletal Muscle Mass in Individuals with, and without, Type 2 Diabetes. Nutrients.
6. Longland et al. 2016. Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial. The American Journal of Clinical Nutrition.
7. Areta et al. 2014. Reduced resting skeletal muscle protein synthesis is rescued by resistance exercise and protein ingestion following short-term energy deficit. Am J Physiol Endocrinol Metab.
8. Helms et al. 2023. Effect of Small and Large Energy Surpluses on Strength, Muscle, and Skinfold Thickness in Resistance-Trained Individuals: A Parallel Groups Design. Sports Med Open.
9. Slater et al. 2019. Is an Energy Surplus Required to Maximize Skeletal Muscle Hypertrophy Associated With Resistance Training. Frontiers in Nutrition.
10. Garthe et al. 2012. Effect of nutritional intervention on body composition and performance in elite athletes. European Journal of Sport Science.
11. Barakat et al. 2020. Body Recomposition: Can Trained Individuals Build Muscle and Lose Fat at the Same Time?. Strength and Conditioning Journal.
12. Barakat et al. 2020, full-text PDF of reference 11 (same review).
13. Antonio et al. 2015. A high protein diet (3.4 g/kg/d) combined with a heavy resistance training program improves body composition in healthy trained men and women – a follow-up investigation. Journal of the International Society of Sports Nutrition.
14. Dr. Antti Rintanen: Does Muscle Weigh More Than Fat? What Density, the Scale and BMI Actually Tell You
15. Dr. Antti Rintanen: RED-S Blood Work and The Female Athlete Triad: A Screening Guide for Coaches and Clinicians

Sources

This tool is based on the articles below and the studies cited in them:

• Is Bulking Necessary for Muscle Gain?
• Muscle Gain Without Fat Gain
• How Much Muscle Do You Lose When Losing Weight?
• Does Muscle Weigh More Than Fat?
• The Leucine Threshold
• RED-S Blood Work
• Mifflin–St Jeor equation (Mifflin et al., 1990)

This tool is for general education. It does not give personal nutrition or treatment recommendations or replace an assessment by your doctor or a dietitian.