The Gait-Speed Signal Behind a Multi-Ingredient ONS

Better walking, unchanged lean mass

A 12-week supplement trial in undernourished older adults produced an intriguing split result: participants walked faster, and muscle biopsies showed higher expression of genes related to oxidative phosphorylation, but lean body mass did not differ significantly from the control group. That pattern may mean functional adaptation can arrive before detectable muscle growth. It does not prove that ursolic acid caused either result.

The 2021 ProMO randomized controlled trial tested a commercial multi-ingredient oral nutritional supplement against a standard casein-only supplement in 82 adults aged 65 or older who were undernourished or at risk of undernutrition, defined by an MNA-sf score below 12. The experimental drink supplied 11 g whey protein, 11 g casein, 7 g free branched-chain amino acids, 10.8 μg vitamin D3, and 206 mg ursolic acid per day. The control supplied casein and differed in vitamin D dose.

The study's pre-specified primary endpoint was lean body mass measured by DXA. It was powered to detect a 1.0 kg between-group difference, assuming a standard deviation of 1.4 kg, with 80% power. It found no significant between-group difference in lean body mass. The intervention group did, however, improve on both 4-meter and 400-meter walking tests relative to control. The publication does not provide the absolute gait-speed difference in the available report, so readers cannot judge whether it reached the commonly used 0.1 m/s threshold for a clinically meaningful change.

That makes the result real enough to take seriously, but too incomplete to market as a muscle-building breakthrough.

Why "function before structure" is plausible

Walking speed depends on more than muscle size. Energy production, coordination, fatigue resistance, inflammation, confidence, and overall nutritional recovery can all affect a timed walk. In a vastus lateralis biopsy subgroup, the ProMO investigators also reported increased expression of oxidative-phosphorylation-related genes in the multi-ingredient group. This is compatible with a change in muscle energy metabolism that precedes measurable hypertrophy.

Nutrition research offers some context for that sequence. A 2023 systematic review of nutrition in sarcopenia describes how nutritional interventions may support mitochondrial activity and muscle performance in older patients. A 2026 meta-analysis of NMN trials likewise reported improvements in muscle and liver functional markers in middle-aged and older adults without consistent lean-mass gains. These findings support a possibility: a supplement can improve some functional measures without adding enough tissue for DXA to detect over 12 weeks.

Possibility is the right word. Increased gene expression is not the same as measured improvement in mitochondrial respiratory capacity. The biopsy subgroup size is also unclear, which limits confidence in the transcriptomic result. A gene-expression signal can reflect improved nutritional status or protein quality; it does not identify the ingredient responsible.

The formulation changed four active variables at once

This is the trial's central limitation. The experimental product did not simply add ursolic acid to the standard drink. It replaced casein-only protein with whey plus casein, added 7 g free BCAAs, increased vitamin D3, and added 206 mg ursolic acid. Each difference could plausibly affect physical function in this population.

A 2023 meta-analysis of whey protein with or without vitamin D found improvements in sarcopenia-related measures, including gait speed and muscle performance, in older adults. Whey is rich in leucine and is digested differently from casein, so switching protein sources is an intervention, not a neutral reformulation. A meta-analysis of whey supplementation during resistance training also found benefits for muscle mass and strength in older people with sarcopenia.

Protein type matters in broader comparisons, too. A 2024 network meta-analysis found that protein supplements differed in effects on muscle mass, strength, and physical measures among older adults undergoing resistance training. And a 2026 meta-analysis of amino-acid supplementation plus resistance training found improved physical function in older adults with sarcopenia. Those studies do not prove that BCAAs alone explained ProMO's walking result, because their intervention settings differed. They do show why the 7 g of free BCAAs cannot be waved away.

Ursolic acid remains the least established component. Laboratory and animal research has proposed several pathways, including mTOR signaling, reduced expression of muscle-specific ubiquitin ligases, and PGC-1α-related mitochondrial biogenesis. No human pharmacokinetic or target-engagement evidence in this trial confirms that 206 mg per day reached skeletal muscle at concentrations that affect those pathways. The human trial tested a package, not ursolic acid in isolation.

Why the participants matter

These were not healthy, well-fed gym-goers looking for an edge. They were undernourished older adults. In that setting, correcting inadequate nutrition can improve performance even without a specialized compound. A 2025 randomized trial of personalized dietary intervention found improvements in nutritional status, muscle strength, physical performance, and quality of life in malnourished older adults, including participants who did not receive structured exercise.

That population makes a functional response clinically relevant. It also narrows generalizability. Someone who already eats adequate protein, has normal vitamin D status, and trains regularly should not assume the same response. The ProMO result may reflect nutritional repletion and better protein quality in a depleted group more than a novel mitochondrial effect.

What resistance training changes

Exercise remains the stronger benchmark for people who can safely do it. A 2023 network meta-analysis of exercise for sarcopenia and a 2024 meta-analysis of resistance training in secondary sarcopenia found that resistance training improves strength, muscle mass, and physical function. A 2021 meta-analysis further found that pairing resistance training with nutritional intervention improves muscle mass, strength, and physical function more than either approach alone.

This comparison helps explain the null lean-mass outcome. Twelve weeks sits at the short end of exercise programs that can detect structural gains, and the ProMO intervention did not provide a resistance-training stimulus. Better nutrition may improve walking before it changes DXA lean mass, but it is also possible that nutrition alone was insufficient to produce hypertrophy.

How much confidence does the trial deserve?

The study was randomized, but it was open-label. Timed walking tests depend partly on effort and expectation, so lack of blinding can bias a secondary performance outcome. The primary endpoint was null, while the headline results came from secondary outcomes. That does not erase the gait-speed finding, but it raises the usual concerns about multiple comparisons and selective emphasis. Independent replication would matter a great deal.

For undernourished older adults, a whey-containing, BCAA- and vitamin-D-containing nutritional supplement may improve walking performance over 12 weeks compared with a casein-only supplement. The trial cannot tell us how much ursolic acid contributed.

The practical conclusion is less exotic than the label. Older adults at risk of malnutrition should address total protein intake, use leucine-rich protein sources such as whey when appropriate, correct vitamin D insufficiency, and add resistance training when medically feasible. The ProMO trial supports nutritional repletion as a useful part of that plan. It does not establish 206 mg per day of ursolic acid as a proven human muscle or mitochondrial supplement.