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As a health coach, I see it all the time. A new client comes to me frustrated and confused. They have been diligently following the perfect diet promoted by a popular content creator — maybe it is keto, maybe it is plant-based, maybe it is intermittent fasting — and they are not seeing the promised results. In fact, some of them feel worse than when they started.
This experience points to a critical, yet persistently overlooked, truth in the world of nutrition: there is no one-size-fits-all diet. And yet, the wellness industry continues to churn out influencers and content creators who confidently declare that their particular way of eating is the way. The problem is not necessarily that they are lying — the approach may genuinely work for them. The problem is that they are presenting an individual result as a universal prescription.
The Problem With Averages
Before we dive into the research, I want to address something that trips up a lot of people when they read nutrition studies. When a study reports that participants lost an average of five pounds on a given diet, that number tells you almost nothing about what you will experience. Averages are a mathematical summary of a group. They smooth over the enormous variation that exists between individuals.
Think of it this way: if you put one hand in a bucket of ice water and the other in a bucket of boiling water, on average you are comfortable. But that is obviously not the reality for either hand. The same logic applies to dietary research. When you look at the individual data points behind a study’s average, you will often find a staggering spread — some people thriving, some people barely responding, and some people moving in the opposite direction entirely.
This is also why the size and diversity of a study’s population matters so much. If a study is conducted on too few people, you cannot reliably pick out a meaningful trend from the noise. And if the study population is not diverse — in terms of age, sex, ethnicity, metabolic health, and lifestyle — then whatever trend does emerge may only be applicable to a narrow subset of people. A finding from a study conducted exclusively on middle-aged men in one country should be applied very cautiously to a 30-year-old woman with a different background and health history.
What the Research Actually Shows
The scientific literature is increasingly clear on this point. Let me walk you through three studies that illustrate just how differently people can respond to the same dietary interventions.
Study 1: Individual Response to Lifestyle Interventions [1]
Researchers pooled data from over 700 participants across three long-term weight loss trials and found that responses were far from uniform. Participants were classified into three groups: those who achieved greater than 5% weight loss (about one-third of participants), those who lost a modest amount, and those who were “weight-loss resistant” — meaning they did not lose weight or even gained some.
Here is what is fascinating: even the weight-loss resistant group showed significant improvements in health markers, including increased HDL (“good”) cholesterol, reduced visceral fat, and lower leptin levels. The scale was not moving, but their metabolic health was improving. This alone should challenge the simplistic view that weight loss is the only measure of dietary success. The researchers also identified specific DNA methylation patterns associated with successful weight loss, pointing to the deep biological individuality that underlies how we respond to diet and lifestyle changes.
Study 2: The DIETFITS Trial [2]
This landmark randomized clinical trial from Stanford University compared a healthy low-fat diet against a healthy low-carbohydrate diet in 609 overweight adults over 12 months. The headline finding was that there was no significant difference in average weight loss between the two groups — the low-fat group lost about 5.3 kg and the low-carbohydrate group lost about 6.0 kg, a difference that was not statistically meaningful.
But the more revealing finding was the enormous range of responses within each group. Weight changes spanned approximately 40 kilograms from the highest loser to those who actually gained weight — and this was true in both diet groups. The researchers specifically tested whether genetic patterns or baseline insulin secretion could predict which diet would work better for a given person. Neither factor was predictive. In other words, even with genetic data in hand, scientists could not tell you in advance which of these two popular diets would produce better results for you as an individual.
Study 3: Heterogeneity in Weight Loss Outcomes in Older Adults [3]
A more recent study examined older adults with obesity who participated in a 24-week telemedicine-delivered diet and exercise program. While participants lost weight on average, the researchers observed what they described as “marked heterogeneity” in physical function outcomes. Improvements in strength, endurance, and energy expenditure varied dramatically from person to person. The coefficient of variation — a measure of how spread out the results were — reached as high as 2,310% for total energy expenditure changes, an almost incomprehensible degree of individual variation.
So What Should You Do?
Given all of this, you should never assume that any given way of eating will produce the results you are after simply because it worked for someone else — or because a study showed an average benefit. Instead, the path forward requires you to become a thoughtful experimenter with your own body. Here is the framework I use with my clients:
Experiment. Approach your nutrition with curiosity rather than dogma. Try a dietary approach for a defined period — at least four to eight weeks — and pay close attention to how your body responds. Focus on whole, minimally processed foods as your foundation, since the evidence for their benefits is robust across populations. For a deeper look at how diet quality can drive body composition improvements, check out my earlier post on Achieving Optimal Body Composition Via Diet Quality Improvements.
Document. Keep a record of what you eat, how you feel, your energy levels, sleep quality, and any other metrics that matter to you. This does not have to be obsessive calorie counting. Even a simple journal noting your meals and how you felt throughout the day can reveal powerful patterns over time. The data you collect on yourself is more relevant to your life than any population average.
Assess. Regularly step back and honestly evaluate your results. Are you moving toward your goals? Are there markers improving even if the scale is not moving as fast as you hoped, as the research above suggests is possible? Be willing to adjust your approach based on what the evidence from your own body is telling you. And remember that your goals themselves should shape your dietary choices — a topic I explore in depth in Why Your Goals Should Dictate Your Food Choices.
The Bottom Line – There Is No Perfect Diet
The next time a content creator tells you that their way of eating is the only way, or that a particular study “proves” you should eat a certain way, take a step back. Ask yourself: what was the range of individual responses in that study? How large and diverse was the population? And most importantly — what does your body tell you when you actually try it?
Science gives us useful starting points and population-level trends. But you are not a population average. You are one person, with a unique biology, history, and set of goals. The most effective nutrition strategy is the one you discover through deliberate, documented experimentation on yourself — not the one that went viral last week.
If you want help navigating that process, that is exactly what I am here for.
References
[1] Meir, A. Y., Tsaban, G., Rinott, E., Zelicha, H., Schwarzfuchs, D., Gepner, Y., Rudich, A., Shelef, I., Blüher, M., Stumvoll, M., … & Shai, I. (2025). Individual response to lifestyle interventions: a pooled analysis of three long-term weight loss trials. European Journal of Preventive Cardiology, 32(16), 1660–1670. https://doi.org/10.1093/eurjpc/zwaf308
[2] Gardner, C. D., Trepanowski, J. F., Del Gobbo, L. C., Hauser, M. E., Rigdon, J., Ioannidis, J. P. A., Desai, M., & King, A. C. (2018). Effect of low-fat vs low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: the DIETFITS randomized clinical trial. JAMA, 319(7), 667–679. https://doi.org/10.1001/jama.2018.0245
[3] Gavras, A., Memili, A., Lynch, D. H., Spangler, H. B., Cook, S. B., Mackenzie, T. A., Gross, D. C., & Batsis, J. A. (2026). Heterogeneity in treatment outcomes after a multicomponent weight loss intervention in older adults with obesity. Current Developments in Nutrition, 10(2), 107649. https://doi.org/10.1016/j.cdnut.2026.107649