Burning fat and gaining mass at the same time
Translated by Janar Rückenberg
Burning fat and building muscle at the same time sounds great, but the body doesn’t usually work in such a straightforward way. If your goal is to lose fat, you need to understand where the energy comes from, why muscle can suffer on a diet and how to keep the damage as small as possible.
Why do fat burning and muscle growth clash?
Many people ask the same thing: can you burn fat and gain mass, meaning build muscle, at the same time? On paper it seems logical. You eat a little less, train properly, add more protein, and the body should supposedly use up fat and build muscle.
The simple truth: fat burning usually requires an energy deficit, while muscle growth requires enough energy and building material. These two directions aren’t always complete opposites, but they pull the body in different directions. This is especially true when you’re not a beginner but have already been doing strength training for some time.
The body doesn’t tap the triglyceride stores deposited in fat tissue very quickly. Even during aerobic training, triglycerides are mobilized fairly slowly. That’s why fat burning is often a long process that demands patience, not a project for a couple of days.
Two things mainly set fat use in motion: physical exercise, especially aerobic work, and a negative energy balance, meaning a situation where you eat less than you expend. These conditions activate lipases, which help release fatty acids and glycerol from the triglyceride molecule. One triglyceride molecule releases three free fatty acid molecules and glycerol. This breakdown of fats is called lipolysis.
Glycerol is water-soluble and moves easily into the blood. That’s why a rise in blood glycerol concentration is a fairly direct hint that lipolysis is taking place. In other words, something has really started moving out of the fat tissue.
It is believed that during a negative energy balance and physical exercise, epinephrine is an important stimulator of lipolysis in fat tissue. Its plasma concentration rises and it activates the beta-adrenergic receptors of adipocytes, or fat cells. It’s dry stuff, but the idea is simple: the body gets a signal that it needs to draw energy from its stores.
Fat burning in training: intensity matters
Physical activity, especially aerobic work, strongly stimulates triglyceride mobilization. During training, the concentration of free fatty acids in the blood rises noticeably. During prolonged physical work, fat oxidation can increase 10 times compared with the resting state.
So what happens when intensity rises to, say, 70% or more of maximal oxygen uptake? Fat oxidation may still increase, but lactate production grows at the same time. Lactate accumulation hinders fatty acid mobilization because it interferes with the enzymes that carry out oxidation.
The more intense the work becomes, the more the emphasis shifts to carbohydrates. At the maximum possible intensity, almost 100% of the energy comes from carbohydrates. That’s why not every training session that leaves you gasping for air is automatically the best fat-burning tool.
At low and moderate intensity, less lactate is produced. In this zone the body can use body fat more calmly, and relatively fewer carbohydrates are used. That doesn’t mean hard training is bad. Rather, it means that when you’re burning fat, the purpose of the training has to be clear: not everything has to be a maximum effort.
Aerobic training creates a favorable environment for fat burning, but only if your nutrition doesn’t work against it. If your calorie intake is high all the time, no amount of easy cardio will save you. If calories are too far in the red, the body starts looking for energy somewhere other than the fat stores.
Does aerobic training eat away at muscle?
Once we’ve restricted calories and created a negative energy balance, the next question comes quickly: can you build muscle at the same time? In most cases the honest answer is that on a diet the main goal is preserving muscle mass, not adding new, high-quality mass.
The body goes after its reserves when food doesn’t provide enough calories to cover the needs of basal metabolism and training. For fat burning, this situation is necessary. But the body doesn’t perfectly choose to burn only fat. To cover the energy deficit, it may also use carbohydrates and proteins.
When carbohydrates are low and the energy deficit continues, insulin production and release are lower. The body releases more hormones such as glucagon and cortisol, whose job is to get energy from various stores. These hormones don’t ask whether your biceps was built up through hard work over the summer. They just do their job.
Translator’s note: Unfortunately, yes, muscle mass falls under that too. For the body, the muscle mass that is so valuable and hard-won for us isn’t actually anything valuable or special; it simply isn’t needed for normal existence. I think increased muscle mass is one of the first things to be targeted in catabolic situations!
Prolonged low insulin, high cortisol and glucagon do not favor muscle mass development. The longer you stay in a negative energy balance, the greater the risk that the body breaks down proteins in various tissues and uses them for energy.
This is where strength training comes in. The best thing you can do to preserve muscle mass during a diet phase is to keep doing intense strength training. Not to pile on endless volume, but to give the muscle a clear reason to stay. If your weights drop quickly, recovery is poor and hunger gnaws at you every day, the deficit is probably too harsh.
Protein, carbohydrates and fat burning on a diet
In bodybuilding, protein targets have been raised during the diet phase for years. This can help, but it is not a magic wand. When amino acids start being used for energy, the body has three main sources.
- Dietary proteins.
- Non-structural free amino acids, which circulate in the body as small reserves.
- Tissue proteins, including the proteins that make up muscles.
Dietary protein covers only a small part of your energy needs, even when protein makes up a large share of the menu. That is why you can’t rely on raising protein intake alone. It helps reduce muscle protein degradation, but it does not stop it completely.
Translator’s note: Of course, many will surely doubt this claim, the author of this note included, all the more so since the entire bodybuilding world uses exactly this tactic when preparing for competitions. But I think we shouldn’t let the claim bother us. The important nuance here is certainly how big an energy deficit we are talking about and how deep into our diet we are. I do believe that on a diet with, say, a 10% calorie deficit, where the deficit has been achieved precisely by cutting carbohydrates, significantly increasing protein intake helps. The body’s protein requirement is covered, and there are indeed resources left over to compensate for the energy deficit. For example, we lower carbohydrates from 3 g to 2.3-2.4 g and raise protein from, say, 2.2 g to 2.6-2.7 g per 1 kg of body weight!
Free amino acid stores in the body are small. These metabolic amino acid resources amount to less than 1%, yet in an energy deficit they are used up quickly. The largest amino acid reserve is in the muscles, in the form of muscle proteins. When the deficit drags on and the training load is high, the body turns there for help fairly quickly.
The main cause of protein degradation is an energy deficit, whether it comes from diet or training. Increased glucocorticoid production makes things worse. When protein intake is low, the risk is even higher. A deficiency of L-leucine can be particularly problematic, because L-leucine is an important amino acid in muscle protein metabolism.
Strength training itself doesn’t build muscle in a vacuum either. Training provides the signal, but afterwards the body needs carbohydrates, amino acids and adequate recovery. Training stimulates the production of anabolic hormones, but if there isn’t enough energy in the cell, that signal does little good. Protein synthesis stays slower and catabolic processes get more room.
Translator’s note: Here, too, it is of course important to point out that everything depends on how you play it, that is, how we manage the diet, how many nutrients we add and in what ratio.
Carbohydrates, aerobic work and a practical plan
Low-carbohydrate diets can work well in the short term, because insulin levels drop and fat storage decreases. But if carbohydrates stay too low for a long time, fatty acid oxidation can also be impaired. An old saying goes that fats burn in the flame of carbohydrates. There is something to it.
A shortage of carbohydrates can interfere with the aerobic energy-production mechanisms. If the body has to rely mainly on fats for too long, the Krebs cycle may slow down. The formation of acetyl-CoA units is disrupted, and with it the whole oxidation process. Not only the use of fatty acids but also their release from the triglyceride molecule may become less efficient.
This doesn’t mean you should eat a lot of carbohydrates on a diet. Rather, they need to be timed wisely. You can keep carbohydrates generally lower, but it’s worth adding them periodically, especially around training sessions. That way you can maintain training quality and signal to your body that the situation isn’t a constant emergency.
In practice, this means three things. First, the deficit should be moderate. A good rate of weight loss would be about 0.5 kg per week. Second, strength training has to stay in, because muscle needs training load to be preserved. Third, it’s worth feeding your muscles after training. The famous carbohydrate window stays open after training sessions during a diet as well.
A post-workout shake of carbohydrates and protein can stimulate insulin secretion. Insulin helps nutrients get into the muscle cell. At the same time, an occasional rise in insulin is also needed so that fat mobilization and oxidation can continue efficiently. Not everything has to be black and white: either zero carbohydrates or eating freely.
In short, fat burning happens thanks to an energy deficit. Gradual fat loss comes from burning more than we eat. But if the deficit is too big, the price gets high: strength drops, recovery gets worse and muscle mass loss increases.
So for most trainees, it isn’t realistic to run a serious fat-loss program and, at the same time, noticeably build quality muscle. The best goal during a diet phase is to keep muscle mass loss to a minimum. You can do that with enough protein, a sensible deficit, keeping up your strength training and post-training nutrition.
FAQ: fat burning and muscle mass
Can a beginner lose fat and build muscle at the same time?
For a beginner, this can happen for a while, because the training stimulus is new to the body. For a more experienced trainee, the same result is much harder to achieve, and the goals usually have to be split into separate periods.
How big a deficit is sensible?
According to the original author, a good rate of weight loss is about 0.5 kg a week. If your weight drops much faster and your strength numbers fall, the deficit may be too big.
Is cardio mandatory on a diet?
It isn’t mandatory, but moderate aerobic training helps raise energy expenditure and support fat utilization. Strength training should still remain the foundation for maintaining muscle mass.
Author: Janar Rückenberg
Come and train! ArtGym
