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The Method N° 09 · Your goal
The deficit takes the fat. Training decides whether the muscle stays.
Every study checked against the paper, . Each section carries its grade. Run the numbers in the app.
Settled
Fat comes off when you take in less energy than you use. That gap is an energy deficit, and nothing else does its job. Fasting windows, fat-burning foods and the time of your last meal only work through what they do to the gap. In a year-long trial of 139 people, adding an eight-hour eating window to the same calorie cut made no difference the trial could tell from chance.1
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Protein is the one number in a diet that protects muscle directly. Outside a deficit, gains from lifting stop rising at about 1.6 g per kilogram of body weight a day.5 In a deficit, for lean people who train, the research points higher: 2.3 to 3.1 g per kilogram of lean mass, which is your weight minus your fat.6
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Lifting is the signal that the muscle is still needed, so it stays in the plan the whole way down. What can give is volume. In trained men eating in a deficit, three sets per exercise kept as much lean mass over six weeks as five did.7 Across the trials, a deficit slowed muscle gain from lifting while strength kept climbing.8
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Adding cardio to lifting does not cost you muscle or maximal strength. It can dull explosive power, mostly when both land in the same session.9 Its job here is to widen the deficit, so you do not have to eat as little.
Still open
In one tightly controlled study, dieters lost the same weight on 5.5 or 8.5 hours in bed. Short sleep cut the fat lost by 55% and raised the lean mass lost by 60%.10 Ten people, two weeks each and no lifting, so treat it as a strong hint rather than a law.
Settled
Training a body part does not burn the fat over it. Across 13 studies and 1,158 people, fat over a trained limb fell no more than over the untrained one.11 Six weeks of ab work, five days a week, did not shift belly fat either.12 Fat comes off where your body takes it from, not where you train. Toning isn't a thing. Muscle is, and so is less fat over it.
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Semaglutide and tirzepatide work by making the deficit easier to hold. In the STEP 1 trial's body-scan group, about 39% of the fat and lean mass lost on semaglutide was lean mass.13 In SURMOUNT-1's, about a quarter of the weight lost on tirzepatide was lean, the same share as on placebo: the drug moved more weight, not a worse mix.14 The two trials measured differently, so these numbers do not rank the drugs. A scan's lean mass includes water and organs, so the muscle share is smaller, but it is real. A 2025 advisory from four medical and nutrition societies pairs these drugs with strength training at least three times a week and enough protein, and says protein without the lifting is likely not enough.15 If you take one, your prescriber should know you train.
Choose Get leaner and the program keeps you lifting the whole way down. When a week in a deficit feels heavier, the next one holds or trims sets instead of piling more on, and your cardio counts against the same weekly ceiling as your lifting.
The research
The 15 sources this chapter stands on, with what each one actually found.
Liu, Huang, Huang et al., 2022 · N Engl J Med
Randomised trial · n = 139 · 12 months
Both groups cut calories by 25%. Adding an 8 a.m. to 4 p.m. eating window: 8.0 kg lost against 6.3 kg, a gap the trial could not tell from chance (p = 0.11).
Read the paper by Liu, Huang, Huang et al., 2022 (opens in a new tab)Garthe, Raastad, Refsnes et al., 2011 · Int J Sport Nutr Exerc Metab
Randomised trial · n = 24 elite athletes · lifting 4 times a week
Both groups lost about 5.5% of body weight. Losing 0.7% a week, the slow group gained 2.1% lean mass; losing 1.0% a week, the fast group lost 0.2%. Bench press rose 13.6% against 6.4%.
Read the paper by Garthe, Raastad, Refsnes et al., 2011 (opens in a new tab)Forbes, 2000 · Ann N Y Acad Sci
Review
The less fat you start with, the larger the share of any loss that comes from lean tissue. A bigger deficit raises that share too.
Read the paper by Forbes, 2000 (opens in a new tab)Helms, Aragon, Fitschen, 2014 · J Int Soc Sports Nutr
Evidence-based recommendations · natural bodybuilders
Lose about 0.5 to 1% of body weight a week to keep the most muscle. A recommendation drawn from the evidence, not a trial of its own.
Read the paper by Helms, Aragon, Fitschen, 2014 (opens in a new tab)Morton, Murphy, McKellar et al., 2018 · Br J Sports Med
Meta-analysis · 49 trials · 1,863 people
Extra protein added to gains from lifting up to about 1.62 g per kg a day, with the true point possibly as high as 2.2. Measured outside a deficit.
Read the paper by Morton, Murphy, McKellar et al., 2018 (opens in a new tab)Helms, Zinn, Rowlands, Brown, 2014 · Int J Sport Nutr Exerc Metab
Systematic review · 6 studies · lean, trained, dieting
2.3 to 3.1 g per kg of lean mass, higher the leaner you are and the bigger the deficit. Few studies, so read the range as a guide.
Read the paper by Helms, Zinn, Rowlands, Brown, 2014 (opens in a new tab)Roth, Schwiete, Happ et al., 2023 · Scand J Med Sci Sports
Randomised trial · trained men · 6 weeks in a deficit
Three sets per exercise against five, eating 30 kcal per kg of body weight: no difference in lean mass or muscle thickness.
Read the paper by Roth, Schwiete, Happ et al., 2023 (opens in a new tab)Murphy, Koehler, 2022 · Scand J Med Sci Sports
Meta-analysis and meta-regression
A deficit shrank lean mass gains from lifting (effect size −0.57) but not strength gains. Around 500 kcal a day was enough to stop lean mass gains: an estimate, not a hard line.
Read the paper by Murphy, Koehler, 2022 (opens in a new tab)Schumann, Feuerbacher, Sünkeler et al., 2022 · Sports Med
Meta-analysis · 43 studies
Adding aerobic training changed muscle growth and maximal strength by effectively nothing. Explosive strength dipped (−0.28), more when both shared a session. A second 2022 analysis found a small cost to fibre growth with running.
Read the paper by Schumann, Feuerbacher, Sünkeler et al., 2022 (opens in a new tab)Nedeltcheva, Kilkus, Imperial et al., 2010 · Ann Intern Med
Crossover · n = 10 · 14 days each
Same diet, same weight lost, about 3 kg. With 5.5 hours in bed instead of 8.5, fat lost fell from 1.4 to 0.6 kg and lean mass lost rose from 1.5 to 2.4 kg. No lifting, and lean mass here includes water.
Read the paper by Nedeltcheva, Kilkus, Imperial et al., 2010 (opens in a new tab)Ramirez-Campillo, Andrade, Clemente et al., 2022 · Human Movement
Meta-analysis · 13 studies · 1,158 people
Fat over a trained limb fell no more than over the untrained one (effect size −0.03). A single small study has argued otherwise, and it stands alone.
Read the paper by Ramirez-Campillo, Andrade, Clemente et al., 2022 (opens in a new tab)Vispute, Smith, LeCheminant, Hurley, 2011 · J Strength Cond Res
Randomised trial · n = 24 · 6 weeks
Seven ab exercises, five days a week: no change in belly fat.
Read the paper by Vispute, Smith, LeCheminant, Hurley, 2011 (opens in a new tab)Wilding, Batterham, Calanna et al., 2021 · N Engl J Med
Randomised trial, STEP 1 · body-scan group n = 140
On semaglutide, fat mass fell 19.3% and lean mass 9.7%. Lean mass was about 39% of the fat and lean lost. A scan counts water and organs as lean, so the muscle share is smaller.
Read the paper by Wilding, Batterham, Calanna et al., 2021 (opens in a new tab)Look, Dunn, Kushner et al., 2025 · Diabetes Obes Metab
Randomised trial, SURMOUNT-1 · body-scan group n = 160 · 72 weeks
On tirzepatide, body weight fell 21.3%, fat mass 33.9% and lean mass 10.9%. About 75% of the weight lost was fat and 25% lean, on tirzepatide and on placebo alike.
Read the paper by Look, Dunn, Kushner et al., 2025 (opens in a new tab)Mozaffarian, Agarwal, Aggarwal et al., 2025 · Am J Clin Nutr
Joint advisory · four medical and nutrition societies
Covers GLP-1 drugs and their combinations. Strength training at least three times a week alongside the drug, with enough protein. Protein without the lifting is likely not enough.
Read the paper by Mozaffarian, Agarwal, Aggarwal et al., 2025 (opens in a new tab)Research describes groups of people. Your coach will tell you how it applies to you.