Personalized Protein May Close the Leucine Gap After 60

The meal-level protein gap is real. The performance benefit is still a question.

Many older adults meet a seemingly reasonable daily protein total yet eat too little protein at breakfast and dinner to reach the per-meal target thought to maximally stimulate muscle protein synthesis. A 12-week Belgian trial found that tailoring a protein supplement to each person's dietary shortfalls increased daily protein, leucine, and energy intake in adults with pre-sarcopenia or sarcopenia. It did not establish that this strategy improves strength, walking speed, or physical function.

That distinction matters. Better intake is a useful result, especially for people who routinely under-eat protein. But a higher leucine number on a food diary is not the same thing as stronger legs, fewer falls, or more independent living.

Why breakfast and dinner can fall short

Older muscle responds less strongly to a small protein dose than younger muscle. In a randomized trial of well-nourished older adults, Murphy et al. describe an estimated requirement of about 0.4 g of protein per kilogram of body weight per meal to maximally stimulate myofibrillar muscle protein synthesis in adults 65 and older. That is about 67% above the 0.24 g/kg/meal estimate for younger adults.

For a 70-kg person, 0.4 g/kg works out to about 28 g of protein at a meal. PROT-AGE guidance, cited in the ENHANce trial, similarly uses roughly 25 g of protein containing 2.5 to 2.8 g of leucine per meal. Leucine is an essential amino acid that helps trigger the muscle-building response to dietary protein.

Community-dwelling older adults often consume only 0.1 to 0.3 g/kg at some meal occasions. Breakfast is the repeat offender: a 2024 scoping review by Khaing et al. found that breakfast has the lowest protein intake across age groups. Dinner can also miss the leucine target, as it did in ENHANce. A bowl of cereal and coffee may be a pleasant morning ritual; it is rarely a 25-g protein meal.

The 2.5-g leucine figure is useful for planning, not a biological tripwire. Wilkinson et al.'s 2023 systematic review found that higher dietary leucine doses were associated with higher post-exercise, post-meal muscle protein synthesis rates. The review also found that protein source, digestibility, and accompanying nutrients change the response. A meal does not become worthless at 2.49 g of leucine.

What the ENHANce trial actually tested

The 2021 ENHANce randomized controlled trial enrolled 51 community-dwelling, Dutch- or French-speaking older adults in Belgium with pre-sarcopenia or sarcopenia. Researchers used habitual food diaries to identify each participant's dietary gaps. Participants received either a personalized protein-supplement prescription designed around those gaps or an isocaloric placebo for 12 weeks.

At baseline, the food diaries showed that participants did not reach the per-meal leucine target at breakfast and dinner. Among the 35 participants who completed the study, personalized supplementation significantly increased total daily protein intake, leucine intake, and energy intake versus baseline. That is a credible proof of concept for identifying a dietary gap and filling it with a targeted supplement instead of handing everyone the same tub of powder.

The trial's most important limitation is its size. Only about 20 completers contributed to functional sub-analyses of handgrip strength, gait speed, and Short Physical Performance Battery scores. Those analyses lacked the statistical power to answer whether the intervention improved physical performance. The study demonstrates improved dietary adequacy; it cannot support a claim of improved function.

There is another complication. The placebo group reduced energy intake significantly (P=0.047), suggesting that even a sham supplement can displace other food. If a real supplement replaces part of a habitual meal, its net benefit at that meal may be smaller than its nutrient label implies. Food diaries can document intake patterns, but they do not settle that question.

Does even protein distribution improve muscle outcomes?

The case for spreading protein more evenly across the day remains plausible but unsettled. A 2021 systematic review by Jespersen et al. found that more even protein distribution was associated with greater muscle mass in healthy adults. It found no association with muscle strength or protein turnover. Because the evidence was observational and cross-sectional, healthier people may simply have had both better muscle mass and more orderly eating patterns. The study cannot show that changing meal distribution caused the difference.

A more direct test produced a null result. In healthy older adults, Justesen et al.'s randomized controlled trial compared even and skewed protein distribution patterns and found no significant difference in muscle protein synthesis or amino acid utilization. That study measured acute physiological endpoints, not long-term strength or disability, and it enrolled healthy rather than sarcopenic adults. Still, it removes any basis for treating even distribution as superior when daily protein intake is otherwise equivalent.

These findings can coexist. A per-meal target may help someone who eats very little protein at breakfast or dinner. Yet once daily protein intake is adequate, shifting grams from one meal to another may not add much. The current evidence does not show that distribution matters as much as total daily protein, nor does it show that a fixed leucine threshold guarantees better function.

Exercise carries more of the functional evidence

The better-supported path to functional benefit combines adequate protein with resistance training. Kirwan et al.'s 2022 systematic review and meta-analysis of randomized trials found that protein interventions augmented resistance exercise effects on appendicular lean mass and handgrip strength in older adults. That evidence concerns protein intervention in an exercise context, not precise meal-by-meal leucine distribution.

Likewise, a 2025 randomized trial in frail older women consuming optimized protein found that resistance training, rather than leucine supplementation, increased basal muscle protein synthesis and reversed frailty markers. The contrast is informative: when protein intake is already optimized, adding leucine alone may not move the outcomes people care about.

Murphy et al. also reported that leucine-enriched protein supplementation did not consistently improve muscle mass, strength, physical performance, or muscle protein synthesis in well-nourished older adults. That does not contradict ENHANce's intake findings. The studies enrolled different populations and asked different questions. It does mean that blanket leucine supplementation makes less sense than addressing a documented dietary shortfall.

A practical, evidence-matched approach

• Check daily intake first. For many older adults, a practical target is at least 1.0 to 1.2 g of protein per kilogram of body weight per day, unless a clinician has advised a different plan for kidney disease or another condition.
• Start with breakfast. Aim for roughly 25 to 30 g of high-quality protein if breakfast is currently light on protein. Dinner deserves the same audit, particularly if it is mostly vegetables, soup, or starch.
• Use food before supplements when practical. Greek yogurt, eggs, dairy, soy foods, fish, poultry, legumes, and protein-fortified foods can help. A supplement is useful when appetite, chewing, convenience, or meal habits make food alone difficult.
• Pair adequate protein with progressive resistance training. This has substantially better support for lean mass, handgrip strength, and frailty-related outcomes than leucine timing alone.
• Do not expect a threshold to act like a switch. Protein quality, the rest of the meal, overall intake, health status, and training all shape the response.

ENHANce supports personalized protein gap-filling as a way to improve protein and leucine intake in older adults with pre-sarcopenia or sarcopenia. It does not yet show that precision supplementation improves strength, gait speed, or physical performance beyond adequate daily protein and resistance exercise.

The sensible move is modest: identify the meals where protein is genuinely low, correct them, and train. Personalized supplementation may make that easier for someone with a real intake gap. The trial that tested it gave a dietary answer. A larger, adequately powered functional trial still needs to supply the clinical one.