BACKED BY SCIENCE: Muscle Gain Prediction – The Muscle to Fat Ratio

Building muscle is a hard and long process which requires a vast amount of patience and consistency. The rate at which muscle is built is dependent on a variety of factors, such as training age, genetics, training programme and nutrition. From a nutrition perspective, it’s been identified on numerous occasions that muscle growth occurs at a much higher rate when adequate energy is available. This is why overfeeding type ‘bulk’ diets are more preferable than calorie restricted ‘fat loss’ diets when attempting to maximise gains in muscle mass and strength. As mentioned previously, it is possible to build muscle whilst in a calorie deficit, but perhaps not optimal. In the short term, catabolic processes are dominant during periods of calorie restriction. Therefore higher rates of protein turnover are observed, thus a reduced capacity to increase muscle size. However as you move from a calorie restricted diet to a calorie surplus diet, these signalling molecules change and the mTOR/anabolic pathway is no longer blunted. Therefore calorie restriction favours catabolism/muscle breakdown, and calorie surplus favours anabolism/muscle growth. Prior to setting goals and starting a ‘bulking’ diet, it’s worth considering the following four studies regarding how much muscle is likely to be built during period of overfeeding.


Rozeneck et al (2002) placed untrained individuals on a 2,000 calorie surplus diet for 8 weeks. When this calorie surplus was combined with a resistance training programme and adequate protein, it was reported that almost all the weight added (3kg) was through increasing muscle mass (not fat mass), where the control group who consumed a maintenance intake didn’t significantly increase muscle mass


Garthe et al (2013), placed elite athletes either on a 500kcal surplus diet, or an ‘ad libitum’ maintenance diet in conjunction with a four day per week hypertrophy focused training programme for 8-12 weeks. As expected, the athletes who consumed a higher calorie intake, gained the most weight, although differences in muscle mass was not considered significant (1.7kg Vs 1.2kg). Moreover and most interestingly, gained the most body fat (1.1kg Vs 0.2kg). Therefore, this does highlight the importance of calorie intake dependant on your training status. I.e. the more trained you are, the less calories you need to build muscle as the additional calorie intake does not favour increased muscle mass and will most likely be stored as body fat instead. AND vice versa. This has been postulated to be a result of untrained individuals having a greater ability to build muscle, and at a higher rate (newbie gains) when compared to their trained/elite athlete counterparts. Therefore requiring more energy to facilitate muscle growth at a higher rate.


Bhasin et al (1996) carried out a landmark study looking at rates of muscle gain where they recruited 40 participants to complete three supervised weight training sessions (4 sets of 6 repetitions) per week for a total of 10 weeks. From a nutrition perspective, calories (36kcal per kilogram of bodyweight and protein (1.5 grams per kilogram of bodyweight) were matched in the different groups; however one group were treated with supraphysiological doses of testosterone where the other group had a placebo (no physiological effect). After the 10 weeks of resistance training, muscle mass in the placebo group had an increase of 1.9kg – where the group treated with high dosages of testosterone gained 6.1kg with no significant change in fat mass between groups.


Bouchard et al (1997) reported that there is inter-individual responses in muscle mass and fat mass during periods of overfeeding.  Over a 100 day period, 24 young and lean men followed a diet where they were overfed by 840kcal per day to facilitate weight gain. During this period, the participants were instructed not to perform any exercise at all. As expected, weight gain was observed where on average 8.1kg of total mass was gained, of which 5.4kg was fat mass and 2.7kg being muscle mass. This provides a nice round figure of a 2:1 ratio in favour of fat gain during periods of overfeeding in lean individuals without any form of resistance exercise. Interestingly, the authors noted that the additional calories consumed over the 100 day period was 84,000kcal, where the total calories stored; 50,220kcal stored as fat mass (9,300kcal per kg), and 2,754kcal stored as muscle mass (1,020 per kg). This leads to only 63% of the energy consumed being stored within the body as either fat mass or muscle mass. Therefore, where did the additional ‘excess’ energy go?


NEAT; Non-exercise activity thermogenesis. This is the term given for energy expenditure that is not related to exercise. This became apparent in a study by Levine et al (1999) where researchers overfed non-obese individuals by 1,000kcal per day above their maintenance intake for eight weeks.  The findings were very interesting. The participants didn’t gain anywhere near as much bodyweight as predicted. This is because two thirds of the energy consume was lost through NEAT. NEAT can be increased through subconscious activities such as; fidgeting and maintaining posture. Therefore, energy intake is elevated and the body is counteracting this by increasing movement in order to preserve leanness.


Bouchard et al (2014) re-examined the data from the previous 1997 study and found characteristics that favoured a higher muscle gain to fat gain ratio. Although 5.4kg and 2.7kg of fat and muscle mass was gained respectively on average, some participants gained more fat and less muscle, where others gained more muscle and less fat. The strongest characteristics that favoured and could be used as baseline predictors for higher gainers in fat mass were; Low levels of muscle mass, low muscle oxidative potential, low VO2 max, low androgenicity, high levels of leptin. The weakest and less consistent predictors were; large abdominal fat cells, low postprandial energy expenditure, high estrogenicity, low DHEA, low cortisol and low thyroid stimulating hormone. Therefore, it could be postulated that if these were reversed, then the ratio of muscle mass to fat mass gain would be more favourable. It’s worth noting that the participants gained muscle without resistance training; since nutrition amplifies the effect of lifting weights. This result is very surprising and unexpected and does raise some questions; were the participants compliant with the ‘no exercise’ rule?  How valid were the measurements taken to measure muscle and fat mass? Are calories far more anabolic than previously thought?


Calorie intake, genetic predisposition, training status and training programme are all major factors when it comes to answering the questions of how fast muscle can be built. It is evident that muscle can be built at a higher rate through overfeeding type diets when compared to their fat loss diet counterparts as a result of energy availability. However, the ratio of which muscle and fat is accrued is far less predictable and a definitive answer cannot be given. In reality, fat gain should be expected when calories are above maintenance where the degree of fat gained is determined by how excessive the calorie intake is. Fundamentally, I would advocate that some fat is gained during a ‘bulking diet’ as this will ensure that sufficient energy is available to build muscle. An attempt can be made to balance the fine line with calorie intake to gain maximal amount of muscle without the fat gain, however there will be an element of uncertainty as to whether the muscle has adequate energy to remodel itself as effectively as possible. It’s more than acceptable if some unwanted fat is gained during this process as it can be lost easily through a calorie restricted diet once the overfeeding phase has finished.


It’s been more than established that a higher calorie intake is required, and that fat gain will most likely happen. However, as reported in the Garthe et al (2013) study, more calories didn’t lead to increased muscle mass, just fat mass. Therefore more doesn’t necessarily mean better when it comes to calorie intake and gains in muscle mass. It would be pragmatic to have calories high enough to promote weight gain, but not so high that body fat gain becomes excessive. If you’re goal is to gain 10kg of muscle mass during an 8-12 week programme like some bodybuilding magazines would suggest, not only will you be disappointed by the reality that you’ll most likely gain 2-3kg, but by the reality that the rest will be fat mass.


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