November 05, 2021 12 min read
Eggs are a very common breakfast item amongst the general population, as well as by physically active individuals as a regular component of a high-protein diet.
Egg yolk comprises ∼40% of the total protein in an egg well as containing several other nonprotein nutrients with potential anabolic effects such as microRNAs, vitamins, minerals, lipids, phosphatidic acid, and other phospholipids suggesting that whole eggs may be a potential food source for enhancing muscle mass, irrespective of its protein content.
Below I will discuss the current evidence as to the effects of whole egg intake on muscle mass, and explore the possible effects of egg yolk compounds that may potentially contribute to skeletal muscle buildup beyond those of egg white alone.
We are well aware that whole eggs are a quality source of protein, but there are many nonprotein nutrients in egg yolk. Besides protein content, egg yolk is comprised of several non-protein nutrients with potential anabolic properties including microRNAs, vitamins, minerals, lipids, palmitic acid, phosphatidic acid, choline, and phospholipids. Below I’ll discuss these nutrients and their potential role in anabolism.
The main phospholipid class found in eggs is phosphatidylcholine, representing ~72% of phospholipids.1
Whole egg is an important food source for this nutrient especially since the habitual intake of phospholipids in thy typical Western diet is only 2-8 grams. Dietary phospholipids and even some modified phospholipid compounds may have anti-inflammatory effects.2
Whole egg intake may potentially decrease inflammatory biomarkers.
The intake of three whole eggs per day reduced tumor necrosis factor-alpha in a study evaluating individuals with metabolic syndrome.3
Tumor necrosis factor is a cytokine – a small protein used by the immune system for cell signaling. If macrophages detect an infection, they release Tumor necrosis factor to alert other immune system cells as part of an inflammatory response.
Another study in overweight individuals showed that C-reactive protein levels were reduced after intake of whole eggs compared to placebo in which both groups underwent a carbohydrate-restricted diet.4
C-reactive protein is found in blood plasma, whose circulating concentrations rise in response to inflammation.
This anti-inflammatory effect does not seem to occur in all populations, such as healthy individuals.5
Since elevated C-reactive protein and tumor necrosis factor-alpha are associated with muscle mass loss,6 scientists think that consuming phospholipids through whole eggs could be a protective factor for muscle maintenance in some populations susceptible to muscle loss (e.g., older adults, people with muscle wasting diseases).
However, this rationale remains to be scientifically proven due to the lack of research evaluating the isolated effects of dietary phospholipids on muscle mass.
Egg yolk also contains phosphatidic acid, a phospholipid investigated for its potential to increase muscle protein synthesis, and muscle mass.7
There is conflicting data in this area of research as some studies show an increase in protein synthesis and muscle hypertrophy from phosphatidic acid supplementation,8 while other studies found no effects on muscle mass gain.9
Therefore, it remains unknown whether the phosphatidic acid consumed through egg yolk may have beneficial effects on muscle hypertrophy.
Omega-3 is a class of polyunsaturated fatty acids with potential effects on muscle mass.10
Mechanistically speaking; omega-3 may enhance the membrane fluidity of muscle fibers, which would improve the uptake of amino acids and make the cell more sensitive to muscle protein synthesis.11
Omega-3 also possesses anti-inflammatory properties,12 which can result in positive effects on muscle mass given that increased inflammation is an established cause of muscle loss.
It is well known that fish oil is the major dietary source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
However, whole egg also contains omega-3 derivatives.
Evidence shows that both young and older adults ingest low amounts of EPA and DHA in the United States.13
Several interventional studies evaluated the effect of high doses of EPA and DHA supplementation (most using fish oil) on muscle mass in young and older individuals.14
Even using doses much larger than those contained in whole eggs, there is conflicting evidence as to whether EPA and DHA intakes have a beneficial effect on muscle mass.10
Therefore, it is unlikely that the EPA and DHA contained in yolk play a primary role in regulating muscle mass.
There is ∼225 mg of cholesterol in the yolk of a medium egg. (McCance &Widdowson, 2004), which plausibly could have indirect anabolic effects, since testosterone is synthesized from cholesterol (Johnson & Wood, 2001).
Testosterone is an anabolic hormone that plays an essential role in the maintenance of muscle mass and strength, and many consumer websites claim that ingesting whole eggs, and consequently cholesterol, is a viable strategy to increase testosterone levels; however, these claims lack a sound scientific basis.15
There is very little evidence evaluating the effect of high dietary cholesterol intake mainly through whole eggs on testosterone levels.
Only one study to date has been completed where they compared the intake of three whole eggs (842 mg/day of cholesterol, being 672 mg exclusively from eggs) versus six egg whites (285 mg/day of cholesterol, being 0 mg from eggs) on testosterone levels in young adults who performed 12 weeks of resistance training.16
The group consuming whole eggs increased testosterone levels by 2.4 ng/ml, while the egg white group increased levels by 0.7 ng/ml.
However, the additional increase in testosterone levels induced by whole eggs intake was not sufficient to enhance gains in muscle mass.16
It is feasible that testosterone fluctuations within the established normal physiological range for men (i.e., ∼300–800 ng/dl) does not have a meaningful impact on human anabolism,17 although some evidence challenges this hypothesis.18
In summary, the limited evidence shows that consumption of cholesterol from eggs may exert some influence on testosterone levels.
I think the slight increase in testosterone from whole eggs is definitely not robust enough to exert an anabolic effect to the point where you would see increase muscle mass/strength.
Egg yolk also contains vitamin D, which is positively associated with muscle mass.19
Besides their natural vitamin D content, eggs can be fortified with D3 and 25(OH)D3 to avoid vitamin D deficiency. Interestingly, a clinical trial conducted in winter with restricted egg intake (≤2 eggs/week) resulted in ∼6–7 nmol/L lower serum 25(OH)D, while seven vitamin D3-enhanced eggs/week or seven 25(OH)D3-enhanced eggs/week maintained the preintervention 25(OH)D levels.
This demonstrates that vitamin D-enhanced eggs can be a viable strategy to maintain 25(OH)D levels.
It doesn’t seem that vitamin D supplementation has any effect on muscle mass, but is does show a small positive effect on muscle strength (mainly in older adults and individuals presenting chronically low vitamin D levels). Since high doses of vitamin D don’t seem to enhance muscle growth; it’s unlikely that vitamin D contained in egg yolk would have any meaningful beneficial effect on muscle mass.
Considering that yolk contains nonprotein nutrients with potential anabolic properties, a recent study compared the effects of whole egg (18 g protein and 17 g fat) versus egg white (18 g protein and 0 g fat) intake on muscle protein synthesis after a resistance training session in healthy young men.20
Whole egg consumption caused a greater stimulation of acute muscle protein synthesis when compared with egg whites.
The increased energy content from whole eggs compared to egg whites may be responsible for the enhanced muscle protein synthesis as increased energy is important to nitrogen balance when exercise is performed.
Although muscle protein synthesis is higher with whole eggs compared to egg white, previous research has shown that acute muscle protein synthesis doesn’t seem to be correlated with muscle growth at an individual level.21
Therefore, it is necessary to evaluate the chronic effects of whole egg versus egg white intakes on muscle mass.
A recent 12-week study compared the consumption of three whole eggs versus an isonitrogenous (i.e., same amount of protein) quantity of six egg whites provided immediately after resistance training in young men.
Results showed that consumption of whole eggs and egg whites promoted similar gains in muscle mass, suggesting that consuming yolk and its nutrients didn’t produce synergistic effects on muscle growth in young men, at least when total protein intake is adequate (study groups consumed ~1.4g/kg per day).16
It’s interesting to note that although results weren’t statistically significant, the whole egg group showed a greater absolute increase in total lean mass (+0.8 kg) compared to the egg white group.
Therefore, current evidence indicates that egg yolk intake likely does not enhance the accretion of muscle mass under protein-equated conditions.
Although findings of a potential benefit on lean mass raise the possibility of an anabolic effect that warrants further investigation.
The discrepancy between the acute and long-term studies could be partially explained because the egg whites and yolks are consumed as part of an overall dietary pattern and many of the aforementioned nutrients contained in whole eggs could also have been obtained from other dietary sources.
Figure adapted from16: Acute and chronic effects of whole egg versus egg whites on muscle mass. Panel (a) is based on a 2017 study20 and (b) is based on a 2020 & 2021 study.16,22 The 2017 study compared the effects of whole egg (18 g protein and 17 g fat) versus egg white (18 g protein and 0 g fat) intakes on MPS after a resistance training session in healthy young men. The 2020 & 2021 studies compared the effects of consumption of three whole eggs versus an isonitrogenous quantity of six egg whites provided immediately after resistance training in young men for 12 weeks. MPS = muscle protein synthesis.
Whole eggs contain a relatively high amount of cholesterol, which is frequently associated with serum lipid concentrations,23 cardiovascular disease and mortality risks.24
A recent analysis of randomized clinical trials showed that the consumption of whole-chicken eggs (∼1–3 eggs per day) increased total cholesterol by 5.6 mg/dl, low-density lipoprotein cholesterol by 5.5 mg/dl, and high-density lipoprotein cholesterol by 2.1 mg/dl.23
However, these increases in total cholesterol and low-density lipoprotein cholesterol do not necessarily lead to cardiovascular events.
When considering the body of evidence to date, a moderate intake of whole eggs (≤3 units per day) doesn’t impact cardiovascular disease and mortality risk.24
It’s crucial to mention that the aforementioned studies analyzed observational data, therefore precluding the ability to find causality on the topic. Some physically active individuals, particularly athletes such as bodybuilders, sometimes consume high amounts of whole eggs, varying anywhere from 0 to 81 eggs per week (~12 eggs/day).25
Since recent data are specific to an intake of 1-3 eggs per day, it’s currently not clear if consumption above this amount is safe.
Due to the scant amount of research, especially placebo-controlled randomized trials; it is not fully elucidated whether egg yolk (or whole egg) has beneficial effects on muscle protein synthesis or muscle mass. Furthermore, the limited research completed was done in young men.
Hence, the effects of whole egg intake on muscle protein synthesis and muscle mass in other populations such as women, older adults, and individuals with muscle wasting diseases remain undetermined. In addition, future research evaluating the effects of whole egg versus egg white intake on muscle protein synthesis should evaluate the effects of yolk intake in individuals consuming higher doses of protein (~.30 g/kg per meal), as well as different amounts of eggs.
Another important point is that future research should assess the chronic effects of egg yolk intake on muscle mass when consuming higher amounts of eggs (>5 units per day) to enhance the intake of yolk nutrients. In addition, future studies should also evaluate the effects of egg yolk intake under conditions both with and without exercise, during bed rest, and when the goal is muscle maintenance or the prevention of anabolic resistance in older adults.
Key points the research seems to indicate are:
Given the extremely scant research on the topic, we can’t make strong inferences to whether egg yolk (or whole egg) has beneficial effects on muscle protein synthesis or muscle mass.
The limited evidence to date demonstrates that egg yolk consumption enhances acute myofibrillar protein synthesis, but these effects don’t seem to translate into improved muscle mass, at least in young men.
As noted, this conclusion is based on very limited evidence and more research is needed in order to draw more robust conclusions not only in young men but also in other populations such as women, older adults, and individuals with muscle wasting diseases.
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