Why should you preserve muscle when losing weight?

Author: Matt Whitaker, Digital Health Lead/11 April 2019

Body composition at the most base level is analysed by identifying contributing quantities of different elements. This however offers little in the way of practical use.

The focus of this blog is on body composition. As analysed by molecular type e.g. water, protein, fats, bones etc.

Lean body mass is principally the entirety of one’s body weight, minus their fat weight, with the largest contributor being water. Another component is total body protein, which is thought to be, on average around 20% of ones total body weight. This protein can be located in virtually every tissue in the body. Including, but not limited to: bone, skin, hair and muscle.

Muscle is largely comprised of proteins and can be subcategorised into: skeletal, which regulate conscious body movement, contractions and posture; smooth, which are not under conscious control and line the walls of organs; and cardiac, which are found exclusively within the heart.

It is not within the scope of this blog to dive any further into the specific qualities of each muscle. But instead the focus will be on skeletal muscle which is involved in the likelihood of sustained weight loss.

Basal Metabolic Rate

The link between muscle mass and sustaining weight loss is an indirect one. The catalyst being basal metabolic rate (BMR) i.e. the amount of energy needed to sustain life. When losing weight it is essential that any reductions in BMR are kept to an absolute minimum. The rationale behind this is as follows. Imagine someone’s BMR is 2000kcal and they reduce their food intake to 1500kcal, creating a 500kcal energy deficit. This leads to short-term weight loss which will inevitably plateau because the individuals BMR reduces to match the new food intake (1500kcal). If the BMR did not reduce there would not have been the plateau in weight loss.

A number of drivers impact BMR when one is reducing body weight. Such as severity of energy restriction, food choice, eating frequency, hormones and exercise routine. All of these variables can also impact muscle mass and indeed, the sustainability of weight loss has been correlated with reductions in muscle mass. The smaller reductions yielding more sustained weight loss, this correlation is also apparent with reductions in BMR. So, where muscle mass is maintained, as is BMR; where BMR is maintained as is the potential to lose weight without hitting a plateau.

Water

Assuming exercise is not present, when one loses weight it is initially chiefly composed of water. This is because the body will use glycogen as its primary energy source and each gram of glycogen can hold onto up to four grams of water. This utilisation of glycogen can easily cause two to four kilos of weight loss in a matter of days. Following this the body will turn to other sources such as fat (primarily) and muscle (inevitably).

When one is losing weight they obviously want near enough all of those lost kilos to be fat. Certainly not muscle. This is of particular importance in overweight/obese individuals who may have poorer muscle quality which adversely affects function. There are a number of ways in which this can be accomplished. At least for the most part- some muscle loss when losing weight is unfortunately unavoidable for most.

Physical activity

Contractile activity is one of the main regulators of muscle protein synthesis and breakdown. This helps to accelerate the process of autophagy (replacing old cellular components with new ones), which maintains muscle function, size and strength. This preserved muscle requires more energy to sustain, meaning reductions in BMR are less apparent. In addition, physical activity can temporarily improve insulin sensitivity. This allow the individual to better access fat stores for energy whilst further potentially inhibiting muscle protein breakdown.

The benefits of resistance training particularly standout in maintaining BMR and even in increasing visceral fat reduction, alongside a host of other benefits previously discussed here.

The impact of endurance activity is less clear in preserving muscle mass when reducing weight. Some research suggests that when combined with diet it is more effective than diet alone, although some muscle loss is still typically observed.

Undertaking any form of physical activity when reducing weight will be a great way to at least minimise reductions in BMR. The most beneficial type is seemingly a resistance training protocol that facilitates progressive overload i.e. leads to continued performance enhancement overtime.

Dietary protein

In the UK, guidance on ‘Reference Intakes’ suggest that we need 50g of protein each day. This is 10% of our total energy intake, in accordance with the same guidelines. The recommendation is appropriate for many who do not regularly take part in physical activity, who are a ‘healthy weight’, eat a variety of ‘complete proteins’ and are not seeking adjustments in body composition, whether this be weight gain or loss.

It has been shown that when one reduces their energy intake, alongside an inadequate protein intake muscle loss accelerates. Therefore, increasing intake of dietary protein when aiming to reduce weight may be wise. And some research has suggested that the muscle sparing effects become most apparent when the protein intake is evenly distributed throughout the day. Aside from potential benefits in muscle protein synthesis, the extra protein may offer an added satiety effect which may make adhering to a new dietary approach more attainable.

It is also suggested that protein quality is equally as important, if not more so than quantity with the guidance of consuming all essential amino acids being recommended. In particular leucine may have a uniquely beneficial muscle sparing effect. Which, if correct leads to the recommendation of ensuring sufficient consumption of any or all of the following: cheese, beef, chicken, pork, nuts, fish, eggs, milk and beans.

Lastly, dietary protein has the highest thermic effect of feeding at ~25%. Meaning 25% of energy taken from protein will be ‘used’ throughout the digestive process.

Intermittent fasting

One of many myths commonly associated with intermittent fasting is that it leads of the breakdown of muscle tissue to be used as energy. When nutrient oxidation partitioning in fasting is examined in research, it is observed that initially the body prioritises carbs which last for one of two days before carb oxidation plummets and fat oxidation upsurges. It is also at this point where protein oxidation (which was negligible anyway) drops further and the body actually becomes more efficient at preserving muscle. This may, at least in part be related to the increments in growth hormone observed when fasting. Additionally, some research has suggested that fasting may upsurge adrenaline, which in-turn increases BMR and may certainly help preserve it.

Protein is a functional tissue, whereas fat is simply stored awaiting use. So preserving protein when fasting entirely makes sense. Furthermore, fat takes far less energy to oxidise. And the body always seeks out the most energy efficient means to survive.

Conclusion

There is a very strong argument for the importance of maintaining muscle mass and BMR when losing weight.

Research has shown the best weight loss results are seen when a dietary intervention (focused on high quality, unprocessed foods) is combined with physical activity in an environment where on-going support is available. More specific recommendations would see combining resistance training with a slightly elevated protein intake and some form of fasting. Practically speaking this could be as simple as doing some basic body weight exercise at home and omitting snacks. Or as comprehensive as following a reputable resistance based gym programme and reducing meal frequency.

Encompassing these recommendations along with overall sustained behaviour change and stress/sleep management (if applicable) may not only enhance weight loss but also physical function and overall health.