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?

It is generally assumed that solid foods are digested more slowly when compared to liquid foods. However, solid foods typically differ from liquid foods not just in food form (liquid vs solid), but also in type of protein, other nutrients, and energy content. Therefore, it was unclear if the form (liquid vs solid) as an isolated factor impacts protein digestion and absorption.

In this study, we compared the plasma amino acid response between 20 g of milk protein as bar or drink in 12 healthy young women. Both products were specifically designed for this study to allow the ingredients to be matched as good as possible.

Key findings:

• The plasma amino acid response did not differ between the liquid and solid treatments
• No differences in hunger ratings were observed between the treatment

What does this mean?

Our data suggest that the food form (solid vs liquid) does not impact the digestion and absorption of protein. It should be noted that the protein bar treatment also drank water (although we don’t think this impacted the results).

Keep in mind that a protein drink and bar are typically not matched for ingredients in practice. Protein bars often contain collagen protein for texture and a chocolate solid outer layer. Therefore, the average protein bar will likely result in a slightly slower digestion and absorption of amino acids when compared to an average protein bar.

Our study:
van Lieshout et al, The Postprandial Plasma Amino Acid Response Does Not Differ Following the Ingestion of a Solid Versus a Liquid Milk Protein Product in Healthy Adult Females, IJSNEM, 2023

Next infographic in the protein series:
High-protein ultra-processed foods result in overeating?

Source: Do protein bars digest slower than protein drinks?

Industrial processing and storage of milk products can cause sugars to bind to amino acids, a process called protein glycation. The essential amino acid lysine is especially sensitive to this, and it’s thought that this may reduce its absorption and bioavailability.

In our new study, we compared the plasma lysine bioavailability of milk protein with a high (50%) vs low (3%) glycation level.

We used specially produced milk protein that included labeled (tracer) versions of lysine, leucine, and phenylalanine. These tracers allowed us to track how much of each amino acid from the milk protein appeared in the bloodstream after digestion and absorption.

Key finding:

• Plasma lysine bioavailability was 18% and 49% for the highly and lowly glycated protein, respectively.
• The bioavailability of leucine and phenylalanine was not affected by protein glycation.

What does this mean?

Our findings suggest that industrial processing and storage of milk protein products can substantially lower the bioavailability of lysine, thereby reducing the nutritional quality of the protein.

Unfortunately, there is no way to know how glycated specific protein products are. But if more research shows glycation can have an impact on protein quality, perhaps it will become common practice to report it on the label. Products that contain both protein and carbohydrate powder are at a higher risk than fluid products such as milk itself.

Link to our study:
van Lieshout et al, Protein glycation compromises the bioavailability of milk protein-derived lysine in vivo in healthy adult males: a double-blind, randomized cross-over trial, Am J Clin Nutr, 2025

Go to the next infographic in the protein series:
Casein protein is not always slowly digested?

Source: Our new study: milk processing lowers protein quality?