The protein-probiotic connection: a match made in heaven?

In my early days, I once managed a gym, and one of the most regular and enthusiastic attendees was a young lad who worked by day as a gardener for the council and trained religiously most nights. He was extremely fanatical about training and his goal was to become as strong as possible. He came in one evening and while chatting to him, I asked how work was going. “I was sacked today” he replied. I asked him why and he explained “I was asked to stack some hay bales this morning but I refused because it would have interfered with my shoulder session at the gym this evening.” The point of this anecdote is to underline just how far some people who are hooked on strength training will go to get gains!

Muscle growth and sleep

When it comes to maximizing strength and muscle gains, many of the nutritional recommendations that have now been confirmed by research were first pioneered by ‘enthusiastic’ experimentation and anecdotal reports emanating from the strength training community. A good example was the practice of consuming milk protein at bedtime, prior to sleep. The rationale used by strength athletes for this practice was simple; during an 8-hour sleep with no protein ingestion, the level of amino acids (the building blocks of proteins) will inevitably decline, thus impairing the ability of muscles to recover and grow following the previous day’s training. The strategy of topping up blood amino acid levels overnight with a slow-digesting protein (eg casein from milk) right before bedtime could help counter this effect, resulting in superior strength and muscle gains.

Like many other intuitive nutritional strategies, it turned out that this was indeed true. A number of scientific studies have since shown that consuming protein just prior to sleeping can enhance muscle mass gains during periods of hard training, and even prevent muscle mass loss during periods when no training is carried out^(1-4).

Incidentally, this ‘protein before bedtime’ effect can also be relevant for endurance athletes. Not only is protein important for endurance athletes for repairing and rebuilding muscle tissue after hard training (for example in running where the continuous pounding action can break down muscle tissue⁽⁵⁾), but it is also needed to build the enzymes and mitochondrial structures (the ‘energy factories’ within muscle cells) that liberate energy in the presence of oxygen, which are made of proteins as well. It’s logical to assume therefore that by consuming extra protein, the regeneration and repair/synthesis of muscle mitochondria could be boosted, and this indeed has been shown to be the case⁽⁶⁾. To read more about the mitochondria-boosting effect of pre-bedtime protein, and which kind of bedtime protein intake is best for endurance athletes, readers are directed to this excellent article by SPB contributor Andrew Sheaff.

More than just protein?

The evidence for ingesting pre-bedtime protein in order to boost muscle mass/strength and to help recovery and mitochondria synthesis in strength and endurance athletes respectively is pretty robust. However, some researchers have speculated that if athletes are going to be consuming pre-bedtime protein, they may get extra benefits from the addition of other nutrients to the protein. One nutrient that may be a candidate for co-ingestion with bedtime protein to aid recovery is a probiotic. That’s because periods of intense training can disrupt the delicate balance of the gut microbiota, which in turn can affect an athlete’s performance and health^(7,8). This can happen because there is a direct relationship and coordination between the gut microbiota and energy metabolism and nutrient absorption.

By maintaining gut health, the energy availability and the structure of the gut microbiota can be improved, thus enhancing the absorption process of nutrients such as amino acids from proteins⁽⁸⁾. There are many pathways by which different strains of probiotics can help activate nutrient absorption from the gut. For example, certain strains such as B. coagulans can improve the health of intestinal mucosal cells by reducing inflammation and promoting optimal development of the villus absorption zone⁽⁹⁾. L. plantarum meanwhile can help maintain intestinal permeability (for the transport of nutrients) and enhance antioxidant capacity⁽¹⁰⁾. It is for this reason that researchers now believe that using a multi-strain probiotic may yield more performance advantages in athletes than single-strain probiotic.

The perfect protein/probiotic combination

If pre-sleep protein enhances recovery and adaptation, and probiotics enhance nutrient absorption, is there a perfect combination, and are the benefits synergistic? Caesin is often recommended for active individuals as a good protein to take before bedtime⁽¹¹⁾. That’s because casein is insoluble in water and coagulates in the stomach, resulting in a much slower amino acid release from the stomach, and therefore a steady increase and more sustained blood amino acid concentration⁽¹²⁾. In this respect, bedtime casein is preferable to the faster releasing whey protein, which is better suited for immediate post-exercise recovery (ingestion of which can be repeated at 2-3 hourly intervals through the day).

What about probiotic intake to accompany casein? One lone study by Jager et al. showed that probiotic supplements combined with casein can reduce muscle damage indicators, improve recovery, and maintain physical performance after intense and damaging exercise⁽¹³⁾. However, the results of other studies giving probiotics are contradictory, finding no difference in swimming performance when Bifidobacterium was supplemented⁽¹⁴⁾, no improvements in the speed, power, strength, and agility of badminton players when Lactobacillus casei was supplemented⁽¹⁵⁾, and no improvements in 1-RM strength (chest press, deadlift, and squat) and vertical jump height of female athletes who took Bacillus subtilis⁽¹⁶⁾.

One explanation for the confusion is that nearly all of the studies on probiotics and athletic performance have utilized only a single strain of probiotic (with or without protein). However, consuming a multi-strain probiotic with casein is known to positively affect protein digestion and absorption. This is turn should be able to accelerate recovery and muscle protein synthesis, while improving the function of the ‘gut-muscle axis’ and balancing intestinal gut flora.

New research

With the above mind, a new study by team of Iranian researchers has investigated the effects of simultaneous pre-bedtime consumption of a multi-strain probiotic plus caesin on athletic performance – specifically anaerobic power, lower-body-specific strength, and power-related performance measures such as sprint speed and acceleration⁽¹⁷⁾. Published in the Journal of the International Society of Sports Nutrition, this study aimed to evaluate the impact of pre-sleep casein intake, combined with multiple probiotic strains on a number of key performance parameters in soccer players playing at an elite level.

Forty-four male soccer players (average age 23 years) were recruited for the study, all of whom were playing in the First Division League of Iran. Before moving onto the experimental phase of the study, all the players underwent a variety of baseline performance tests. These were:

·        Wall squat test (holding a static position)- a practical and reliable method to assess lower-body isometric strength and endurance, targeting critical muscle groups such as the quadriceps, hamstrings, and gluteal muscles.

·        Isokinetic strength testing – to assess absolute peak muscle torque (APT), relative peak torque (RPT), average peak torque (AvPT), time to peak torque (TPT), and average rate of force development (AvRFD).

·        Running-based anaerobic sprint (RAST) tests- to assess anaerobic maximum (RAST max power), anaerobic average (RAST avg power) and anaerobic power-to-weight ratio.

The intervention protocol

In the 4-week intervention, the soccer players were randomly divided into four groups of 11, which were as follows:

·        Probiotics only – where the players were given one probiotic capsule (containing eight bacterial strains: Lactiplantibacillus plantarum BP06, Lacticaseibacillus casei BP07, Lactobacillus acidophilus BA05, Lactobacillus bulgaricus BD08, Bifidobacterium infantis BI04, Bifidobacterium longum BL03, Bifidobacterium breve BB02, and Streptococcus thermophilus BT01), with a total dose of 4.5 × 10¹¹ colony forming units [CFU]) at dinner time.

·        Casein only – where the players consumed 20 grams of casein powder 45 minutes before retiring for bed.

·        Probiotics + casein – where the players were given one probiotic capsule at dinner and 20 grams of casein powder 45 minutes before bedtime.

·        Placebo – where the players were given one red capsule (containing grams of inert starch) during dinner.

All participants were instructed to take the supplements only on training days (three times a week), where they continued with their soccer training. At the end of the 4-week intervention, the baseline tests were repeated to investigate what differences (if any) had occurred. Figure 1 shows the overall study protocol.

Figure 1: Testing and intervention protocol