Does a self-selected vegan diet result in muscle loss in older adults?

Vegan diets are increasing in popularity, mostly for health, ethical, or sustainability reasons. However, plant-based food sources are often relatively low in protein. In addition, plant-based sources are typically of lower protein quality than animal-based sources, because of lower digestibility and suboptimal amino acid composition.

When protein intake is strictly matched, most studies find no meaningful differences in muscle protein synthesis or muscle mass when comparing vegan and omnivorous diets, suggesting that protein quality is not always impactful. However, what happens when people adopt a vegan diet freely (self-selected)?

This study investigated the impact of a 12-week self-selected vegan diet versus an omnivorous diet on muscle protein synthesis and muscle mass in older adults. Participants had monthly nutrition meetings where they received guidance to adopt the vegan diet.

Muscle protein synthesis was assessed over a 10-day period at the start of the intervention using labeled water (D2O). Muscle mass was determined with MRI. 

Key findings:

• The vegan diet resulted in a reduced protein intake (from 1.0 to 0.7 g/kg/day)
• The vegan diet had 14% lower muscle protein synthesis
• The vegan diet reduced muscle mass by 5%

Interpretation?

This study shows that a self-selected vegan diet lowers protein intake and muscle mass in older adults. These findings highlight the importance of maintaining total protein intake when switching to an all plant-based diet.

Strengths of this study include the measurement of muscle protein synthesis over 10 days using D2O and the assessment of muscle mass with MRI. In addition, external validity is high, as the diet was self-selected. A limitation is that the diets differed in many nutrients, making it difficult to determine whether and to what extent each nutrient contributed to the results.

Link to study:
Domić J et al., Does a self-selected vegan diet result in muscle loss in older adults? Am J Clin Nutr, 2026

Go to the next infographic in the protein series:
Chewing increases protein synthesis?

Q1: Does this mean you will always lose muscle mass on a vegan diet?
No. When protein intake is high and matched, studies generally find no clear disadvantage of a vegan or vegetarian diet. The key message of this study is that a vegan can reduce muscle mass if protein intake drops.

Q2: What is the practical implication?
Make sure protein intake does not drop when switching to a vegan diet. Participants in this study received guidance from a dietician, including a session focused on protein, and their intake still dropped by ~30%. So don’t assume protein intake will be fine: check it. Be especially careful when recommending a vegan diet to others, who may be less knowledgeable or motivated.

Q3: Is this study consistent with literature?
Mostly yes. Most studies on this topic matched protein intake to isolate the impact of protein quality. The few studies of self-selected vegan diets also tend to find lower protein intakes.

Q4: How large is this effect?
Muscle mass declined by ~5% in the vegan diet. After age 50, ~1% of muscle mass is lost per year. So this 3-month vegan diet caused roughly the equivalent of 5 years of age-related muscle loss.

Q5: What were some of the other findings?
The vegan diet increased fiber intake by 45% and reduced body weight (3kg), visceral fat (9%), and liver fat. Focusing only on muscle would oversimplify diet choice: the best diet may depend on which outcome matters most for the individual (e.g. risk of frailty vs cardiovascular disease).

Q6: Did energy intake play a role?
Probably. Reported energy intake did not change, but the vegan group lost 3 kg (of which 1.2 kg aLBM), suggesting a caloric deficit. A possible explanation is lower energy absorbed due to the higher fiber intake. An energy deficit makes muscle loss more likely.

Q7: What can the third group teach us?
The third group combined the vegan diet with resistance exercise. They still lost muscle, but less than the vegan group without exercise (3 and 5%, respectively). So, exercise partly offset, but did not prevent, the effect of lower protein intake and quality.

Does this study change how you think about vegan diets and muscle health? Have questions about the study or its interpretation? Drop them in the comments.

Source: Does a self-selected vegan diet result in muscle loss in older adults?

A “bubble gut” is often seen in high-level bodybuilders on stage, despite them having extremely low body fat levels. The reason for this is still unclear, but enlarged abdominal muscles, enlarged internal organs, and/or visceral fat between the organs may contribute.

It also remained unclear what is causing these bubble guts. It has been speculated that very high protein intakes and/or anabolic-androgenic steroids (AAS) play a role.

In our new study, we used MRI to assess organ volume in:

• Recreationally active males (control)
• Competitive male natural bodybuilders
• Competitive male bodybuilders using AAS (enhanced bodybuilders)

Key findings:

• The natural and enhanced bodybuilders had approximately double the protein intake when compared to the controls (2.5 and 2.9 vs 1.4 g/kg/d)
• Internal organ sizes were not greater in the natural bodybuilders compared to the control group, but the enhanced bodybuilders had substantially larger organs.

Interpretation?
Although the natural bodybuilders had much higher protein intake and greater lean mass when compared to the healthy controls, their organs were not larger. Because only the enhanced bodybuilders showed an increase in organ size, this suggests that AAS may be the primary contributor to the bubble gut.

Strengths and limitations
A strength of this study was the use of whole-body MRI to assess the actual size of several organs. A limitation is that it was a cross-sectional study, meaning that cause-and-effect cannot be proven.

Link to our study:
Fuchs et al, When Size Goes Inside: Visceromegaly in Bodybuilders Is Not Attributed to High Protein Intake but More Likely Associated with the Use of Appearance- and Performance-Enhancing Drugs, Med Sci Sports Exer, 2026

Go to the next infographic in the hormone series:
Testosterone injections increase organ size?

Source: Anabolic-androgenic steroids increase organ size?

Carrots get their orange color from beta-carotene. When consumed, beta-carotene is absorbed and accumulates in the skin and subcutaneous fat, giving the skin a subtle yellow-gold tone. Researchers call this effect “increased skin yellowness”, informally better known as a “carrot tan”.

A carrot tan is consistently rated as attractive, possibly because it signals current health and micronutrient status.    

This study used software to create controlled versions of the same face. These faces differed only in skin color: higher or lower carotenoid-related yellowness, or lighter or darker melanin-related skin (tanned or genetically darker skin).

Key findings

• Carotenoid-rich skin was preferred over low-carotenoid skin (~86%)
• Melanin-rich skin was preferred over low-melanin skin (~79%)
• Carotenoid-rich skin was preferred over melanin-rich skin (~76%)

Interpretation
These data suggest that very pale skin is generally rated as less attractive. While tanned skin is found more attractive than pale skin, carotenoid-rich skin is considered even more attractive. Pale skin may signal lower health, while tanning may partially mimic the visual effect of carotenoids or mask a low carotenoid status.

Strengths
The study included three complementary experiments and a relatively large sample size.

Limitations
Face variants were created digitally rather than from real interventions. Also, the carotenoid skin tone tested represented an “optimal” hue from pilot testing. It is unclear whether more extreme carotenoid tones would be equally attractive or less attractive. Finally, the participants were predominantly white, the experiment was conducted in the UK, and cultural differences may influence results.

Link to study:
Levefre et al., Fruit over sunbed: carotenoid skin colouration is found more attractive than melanin colouration. Q J Psychol (Hove), 2015

Source: Carotenoids increase skin tone attractiveness?

Some training philosophies, such as High-Intensity Training (HIT), propose that one set taken to failure is enough to maximize muscle growth. Others have suggested that more sets always produce more gains.

This study investigated the effect of resistance exercise volume on muscle protein synthesis (MPS; the process driving muscle adaptations such as growth). Resistance-trained males performed a unilateral exercise protocol in which each leg completed a different condition, randomly assigned to:

• 1 set unilateral leg extensions to failure
• 3 sets of unilateral leg extensions to failure

MPS was measured in the early phase (first 5 hours post-exercise) and the next day (24-29 hours post-exercise).

Key findings:

• Three sets produced a greater rise in early-phase MPS than one set.
• The next day, MPS remained elevated in the three-set treatment, whereas it had returned to baseline in the one-set treatment.

Interpretation

Even a single set of resistance exercise results in a clear increase in MPS. However, three sets elicit a greater and longer-lasting MPS response. This suggests that resistance training volume (number of sets) is an important driver for muscle growth and that very low volumes may be suboptimal.

A strength of this work is the unilateral study design, which enables a direct within-participant comparison of 1 vs 3 sets, thereby minimizing the influence of genetic and motivational factors.

A limitation is that muscle protein breakdown was not measured, even though it may also increase with a higher training volume.

Link to study:
Burd et al., Resistance exercise volume affects myofibrillar protein synthesis and anabolic signalling molecule phosphorylation in young men. J Physiol, 2010.

Go to the next infographic in the resistance exercise series:
Rep ranges are not critical for muscle growth?

Source: Resistance exercise volume increases MPS?

Endurance training improves oxygen uptake and mitochondrial function. Interval training is often promoted as a time-efficient alternative to steady-state cardio, and some claim it might even stimulate greater muscle growth.

We compared High-Intensity Interval Training (HIIT) and Moderate Intensity Continuous Training (MICT) over two weeks. Myofibrillar protein synthesis rates were assessed, reflecting muscle contractile proteins. Each of the ten subjects trained one leg with HIIT and the other with MICT, with both protocols matched for total volume and duration.

Key findings:

• Single-leg maximal workload and VO2_peak improved with both HIIT and MICT.
• Myofibrillar protein synthesis did not differ between HIIT, MICT, or the control period.

Interpretation
Even though HIIT had a higher exercise intensity, it did not increase muscle protein synthesis rates more than MICT. In fact, neither training mode increased muscle protein synthesis rates compared to the control period, during which participants performed daily physical activity.

These findings suggest that even higher-intensity endurance exercise is not a strong stimulus for muscle protein synthesis. This aligns with long-term studies showing minimal impact of endurance exercise intensity on gains in fat-free mass.

A major strength was the one-leg within-subject design with volume- and duration-matched protocols, which allowed a clean comparison of exercise intensity. Limitations included the fact that single-leg cycling does not reflect real-world training and that habitual physical activity was not controlled.

Link to our open-access study:
Trommelen et al., Daily Myofibrillar Protein Synthesis Rates Do Not Differ During Interval Compared to Continuous Exercise Training Matched for Duration and Work in Healthy Young Men. IJSNEM, 2026.

Source: Interval more anabolic than continuous cardio?

Exercise provides many health benefits and can improve fitness and appearance. Yet, many people do not exercise regularly.

This study investigated the impact of educational and planning strategies on exercise participation. Participants (n=248 university students) were randomly assigned to three groups. Exercise sessions were measured over the week following the intervention.

1. Control: reading a neutral text (first three paragraphs of a novel)
2. Motivation: reading a leaflet with information about the health benefits of exercise
3. Planning: received the same leaflet plus completed a planning task specifying what, when, and where to exercise

Key findings:

• Education alone increased the motivation to exercise but did not increase actual exercise participation; many participants reported being ‘too busy to exercise’.
• Education combined with a planning task increased both motivation and actual exercise participation (91% of participants exercised at least once in the week following the intervention).

Interpretation
This study shows that information alone can increase motivation, but that this does not always lead to behavior change. Even motivated individuals may fail to act. Creating a specific plan, such as deciding what, when, and where to exercise, can help turn intentions into action. This strategy, known as implementation intentions, has been shown to work for other behaviors as well.  

A strength of the study was the large sample size. Limitations include the very short study duration (1 week) and the outcome was based on self-reported sessions (not objectively verified).

Study:
Milne et al. Combining motivational and volitional interventions to promote exercise participation: protection motivation theory and implementation intentions. Br J Health Psychol, 2002

Source: Motivation alone is not enough?

Sugar is highly palatable and energy-dense, which can contribute to excess calorie intake. A common strategy to reduce sugar consumption is to replace it with low- or no-calorie sweeteners, which provide sweetness without the associated energy.

Although sweeteners are generally considered safe, public concerns remain regarding their effectiveness and potential health risks. Some studies have suggested that sweeteners may be ineffective for weight management or could negatively affect gut health. The evidence is conflicting, likely due to differences in study design.

This randomized controlled trial examined the long-term effects of sweeteners on weight loss maintenance, cardiovascular health, and the gut microbiome.

Participants (341 adults and 38 children) with overweight or obesity first followed a two-month weight-loss diet, achieving at least a 5% reduction in body weight. They were then assigned to a 10-month healthy diet phase:

• The sugar group was allowed <10% of total energy from sugar.
• The sweetener group replaced sugar with sweeteners as much as possible

Key findings after the 12 months:

• The sweeteners group maintained greater weight loss (1.6±0.7 kg).
• The sweeteners group showed beneficial changes in the gut microbiome.
• No significant differences between the groups were observed for cardiometabolic health markers.

Interpretation:
This large-scale trial indicates that replacing sugar with sweeteners helps maintain weight loss. Moreover, the use of sweeteners did not adversely affect cardiometabolic health and improved the gut microbiome.

Strengths of this study include its long study duration (12 months), large multi-national sample size (379 participants), inclusion of multiple sweeteners and commercial products, and the replacement of sugar with sweeteners within a generally healthy diet. A limitation is that, because commercial products were used, blinding of subjects was not possible.  

Link to study:
Pang et al., Effect of sweeteners and sweetness enhancers on weight management and gut microbiota composition in individuals with overweight or obesity: the SWEET study. Nat Metab, 2025

Source: Sweeteners help maintain weight loss?

PFAS (“forever chemicals”) are synthetic compounds used in products like nonstick pans and firefighting foams. They stick around in the body for years (half-life is approximately 5 years) and have been linked to adverse health effects, although the exact risk thresholds are still debated.

Until recently, no strategy was known to lower PFAS levels in humans.

This study tested whether regular blood or plasma donations could impact PFAS levels in firefighters (who often have elevated levels).

What they did:

• Whole blood donation group: 470 ml every 12 weeks
• Plasma blood donation group: 800 ml every 6 weeks
• Control group: no donations

What they found after a year:

• Whole blood donors: 10% decrease in blood PFAS
• Plasma blood donors: 25% decrease in blood PFAS
• Control group: no change

What does this mean?

Both whole blood and plasma donations reduce PFAS levels in people with high exposure. Plasma donation seems to work best, likely because PFAS concentrate more in plasma and because donations were more frequent and larger in volume.

Link to study:
Gasiorowski et al., Effect of Plasma and Blood Donations on Levels of Perfluoroalkyl and Polyfluoroalkyl Substances in Firefighters in Australia, JAMA Netw Open, 2022

Source: Can blood or plasma donations reduce plasma PFAS levels

Ultra-processed foods drive overeating, but adding protein is often marketed as a fix.

This study compared two ultra-processed diets: high protein vs normal protein (3.3 vs 1.5 g/kg/d).

Participants lived in a metabolic chamber for 2.5 days with plentiful access to each diet (they could eat as much as they wanted). Both energy intake and expenditure were measured to assess energy balance.

Key finding:
The normal-protein diet led to a positive energy balance of 32%, while the high-protein diet cut this down to 18%.

So more protein helped, but didn’t fix the problem. Ultra-processed diets, high in protein or not, still promote overeating.

That said, these products can still be useful for specific groups, such as clinical patients or athletes who struggle to meet both their caloric and protein intake requirements.

Link to study:
Hagele et al, Short-term effects of high-protein, lower-carbohydrate ultra-processed foods on human energy balance. Nat Metab, 2025

Source: High-protein ultra-processed foods result in overeating?

Exercise stimulates the uptake of blood sugar (glucose) into the exercised muscle. But does it affect glucose uptake in other muscles that have remained rested?

This study tested how one-legged exercise affects glucose uptake in exercised and nonexercised muscle. The exercise session consisted of one-legged knee extensions until exhaustion (around 2.5 h).

Glucose uptake was assessed with an insulin clamp on two different days:

• Day 1 (Rest): non-exercise leg
• Day 2 (Exercise)
  • Exercised leg
  • Non-exercised leg

Key findings:

• Glucose uptake increased by 17% in the exercised muscle
• Glucose uptake decreased by 37% in the nonexercised muscle
• Whole-body glucose uptake decreased by 18% compared to the rest day

What does this mean?

Exercising a muscle boosts glucose uptake in that muscle, but lowers it in muscle you did not exercise. This may be beneficial to direct glucose towards the muscle that needs it for glycogen recovery.

Surprisingly, whole-body glucose uptake appeared to decrease following one-limbed exercise. This counterintuitive finding is important for people with diabetes who need to regulate their blood sugar.

It remains to be determined if exercising a muscle also steals other nutrients. For example, don’t train legs because you want all the amino acids to go to your arms.

Link:
Steenberg et al. A Single Bout of One-legged Exercise to Local Exhaustion Decreases Insulin Action in Nonexercised Muscle Leading to Decreased Whole-Body Insulin Action. Diabetes, 2020.

Source: Do exercised muscles steal nutrients from non-exercised muscles?