Scientists want to understand how diet affects aging, but they’re running into a big problem: finding young, healthy people willing to participate in long-term nutrition studies is surprisingly difficult. Researchers studied how to recruit participants for a diet and longevity study and found that only about 3-4 out of every 100 people who applied actually qualified and enrolled. The main barriers were strict health requirements and people’s unwillingness to stick with demanding diet changes for extended periods. This research shows that future studies about food and aging will need smarter recruitment strategies to find and keep participants interested.

The Quick Take

  • What they studied: How difficult it is to recruit young, healthy adults for studies that test whether different eating patterns can help people live longer and healthier lives
  • Who participated: 70 young adults (ages 25-49) with normal body weights who were not taking medications, recruited across two research sites. Researchers also surveyed nearly 500 other adults to understand general interest in diet and aging studies
  • Key finding: Only 3-4 out of every 100 people who applied to the study actually qualified and enrolled. When researchers looked at national health data, they found that only about 3.6% of American adults even met the basic eligibility requirements
  • What it means for you: If you’re interested in participating in nutrition research, understand that these studies have strict requirements because they need very specific types of participants. Future studies may need to relax some requirements or offer better incentives to recruit enough people

The Research Details

This was a practical study that looked at real-world challenges in recruiting people for a diet and longevity research project called DiAL Health. The researchers tracked how many people applied, how many qualified, and how much it cost to enroll each participant at two different research locations. They also analyzed national health survey data from 2017-2020 to see what percentage of American adults would even be eligible for such studies. Finally, they surveyed nearly 500 adults to understand whether people were actually interested in participating in diet studies focused on aging.

The study examined two main things: the practical recruitment numbers and costs, and people’s actual willingness to participate in different types of diet studies. Researchers asked survey participants whether they’d be willing to try time-restricted eating (eating during limited hours), caloric restriction (eating fewer calories), or other dietary approaches, and whether they’d stick with these changes for different lengths of time.

This approach is valuable because it combines real enrollment data with national statistics and direct feedback from potential participants, giving a complete picture of the recruitment challenge.

Understanding recruitment challenges is crucial because scientists can’t study how diet affects aging without enough young, healthy participants. If researchers don’t know why recruitment is difficult, they can’t fix the problem. This study identifies the specific barriers—strict eligibility requirements and low public interest in long-term diet studies—so future researchers can develop better strategies.

This study provides real, practical data from actual recruitment efforts, which is valuable. However, it’s important to note that the findings come from just two research sites, so results might differ in other regions. The survey of 492 adults is a reasonable sample size, but it represents only a snapshot of American attitudes. The use of national health data (NHANES) strengthens the findings by showing that the recruitment challenge isn’t unique to these two sites—it reflects a real characteristic of the American population.

What the Results Show

The researchers found that recruiting young, healthy adults for diet and aging studies is significantly harder than expected. Out of 2,049 people who applied to the study, only 70 actually enrolled—a success rate of just 3.4%. This means roughly 97 out of every 100 applicants didn’t make it into the study.

The cost to recruit each participant varied dramatically between the two research sites: $1,572 per person at one location versus $625 at the other. This suggests that recruitment strategies and local factors make a big difference in both success rates and expenses.

When researchers looked at national health survey data, they discovered an even bigger problem: only 3.6% of American adults meet even the basic eligibility criteria for these types of studies. The criteria weren’t extreme—participants needed to be relatively young, have a normal to slightly overweight body mass index, and not be taking medications. Yet this combination of requirements eliminates most of the population.

The survey revealed another important finding: while young adults expressed interest in participating in diet studies, their willingness dropped significantly when studies required longer time commitments or more restrictive eating patterns. People were more willing to try time-restricted eating than strict calorie counting, and more willing to participate in shorter studies than longer ones.

The research identified that the strictest eligibility requirements—particularly the requirement that participants not be taking any medications—eliminated a large portion of potential recruits. Many otherwise healthy young adults take medications for conditions like high blood pressure, high cholesterol, or mental health, which disqualified them. Additionally, the study found that body weight requirements, while reasonable for studying aging, still excluded many interested applicants. The formative survey showed that only 2.2% of survey respondents met all the study’s eligibility criteria, which is even lower than the 3.6% found in national data, suggesting that self-selected survey respondents weren’t necessarily more likely to qualify.

This research addresses a gap in the scientific literature by directly examining recruitment challenges for aging and nutrition studies. While previous research has discussed the importance of long-term dietary intervention trials, few studies have systematically documented how difficult it is to actually recruit participants. The findings align with general knowledge that recruiting healthy, unmedicated young adults is challenging, but this study provides concrete numbers and costs that quantify the problem. The results suggest that many previously published nutrition studies may have faced similar recruitment barriers, which could affect how representative their findings are of the general population.

The study has several important limitations. First, it only involved two research sites, so the recruitment challenges and costs might be different in other parts of the country. Second, the survey of 492 adults, while useful, represents only a small snapshot of American attitudes and may not reflect all demographic groups equally. Third, the study doesn’t deeply explore why people declined to participate beyond basic interest in different diet types—there may be other barriers like time constraints, skepticism about research, or lack of awareness. Finally, the NHANES data used for comparison came from 2017-2020, so it may not reflect current population characteristics. The study also doesn’t account for seasonal variations in recruitment or differences in how actively each site promoted the study.

The Bottom Line

Based on this research, future diet and aging studies should: (1) Consider relaxing some eligibility requirements, particularly the requirement that participants take no medications, unless those medications directly affect the research question; (2) Invest in targeted recruitment strategies that reach specific populations more efficiently; (3) Design studies with shorter time commitments when possible, since people are more willing to participate in brief interventions; (4) Budget significantly more resources for recruitment than might be expected—the $625-$1,572 per participant cost should be factored into study planning; (5) Use multiple recruitment channels and strategies, since the two sites in this study had very different success rates and costs. These recommendations have moderate confidence because they’re based on real recruitment data, though they may need adjustment for different populations or study designs.

This research matters most to scientists and research institutions planning nutrition studies, as it provides practical guidance for budgeting and planning. It’s also relevant to people interested in participating in research—understanding these challenges explains why some studies have strict requirements. Healthcare providers should be aware that recruitment barriers may limit the diversity of participants in nutrition research, which could affect how well findings apply to all populations. The general public should understand that participating in research studies requires meeting specific criteria for scientific reasons.

The recruitment challenges identified in this study are ongoing and won’t change quickly. However, if researchers implement the suggested strategies—like relaxing some requirements or designing shorter studies—improvements could be seen within 1-2 years of new studies launching. For individuals interested in participating in diet studies, understanding these barriers means being prepared for strict screening processes and potentially waiting for studies that match your situation.

Want to Apply This Research?

  • If using a nutrition app and interested in research participation, track your current diet pattern (meal times, calorie intake if relevant) and any medications or supplements you take. This baseline data helps you understand whether you might qualify for future studies and allows you to see changes if you decide to modify your eating habits.
  • Use the app to experiment with time-restricted eating windows (eating during specific hours) or track meal timing, since this study found people were more willing to try time-restricted eating than other diet approaches. Start with a small change, like eating within a 10-hour window, and track how it affects your energy, hunger, and overall wellbeing.
  • Set up weekly check-ins in the app to monitor your eating patterns, energy levels, and any changes in how you feel. If you’re considering participating in a diet study, maintain consistent tracking for at least 2-4 weeks to establish a baseline. This data can be valuable both for your own awareness and potentially for researchers evaluating whether you’re a good fit for their studies.

This research describes challenges in recruiting participants for nutrition studies and does not provide medical advice or dietary recommendations. The findings are about research methodology, not about what diet you should follow. Before making any significant changes to your diet or eating patterns, consult with your healthcare provider. If you’re interested in participating in nutrition research, discuss this with your doctor to understand whether you might be eligible and whether participation is appropriate for your health situation. This study was published in a peer-reviewed journal but represents one research team’s experience; results may vary in other settings or populations.