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If nutrition depended only on general rules, dietitians would have an easy job. In practice the same foods affect people differently, and an industry has grown around that: apps that track glucose, microbiome tests, DNA kits, AI assistants that analyze a photo of your plate. What of this is supported, and what is just nicely packaged?
What the science shows
The best-known study is PREDICT, run by King’s College London and other centers. It showed that responses to identical food vary a lot between people: glucose and lipids after a meal depended not only on the meal’s composition but also on sleep, time of day, physical activity and the microbiome, while genetics explained only a small share of the differences (Berry et al., Nature Medicine, 2020). The idea that one size fits all really is weak.
It does not follow that a personal algorithm always beats a simple rule. Studies where people received personalized glucose-based advice showed modest improvement in some participants, and large head-to-head comparisons with good baseline advice are scarce.
What actually scales
Fiber. High fiber intake is consistently linked in large reviews to lower risk of cardiovascular disease and type 2 diabetes. Most people worldwide eat less than the recommended 25-30 g a day.
Protein. Older adults and people who lift need more than young sedentary people: a range of 1.0-1.2 g per kg of body weight and above is often cited, but your individual target should come from a doctor, especially if you have kidney disease. More on the link to muscle in our piece on strength training .
Ultra-processed food. In a controlled NIH study by Kevin Hall (2019), participants on an ultra-processed diet ate roughly 500 kcal a day more than on a minimally processed one and gained weight. That does not make all such food harmful, but it points to a mechanism of overeating.
Where technology really helps
- Food recognition from photos. AI identifies a dish well but gets portions and composition wrong. Good for building a logging habit, not for precise counting.
- CGM for a limited time. Helps you see your own responses; see the piece on glucose sensors .
- Microbiome analysis. The market is ahead of science: there are no firm dietary recommendations from standard tests yet, and results depend on the lab and method.
- Genetic nutrition tests. Justified for rare conditions (lactose intolerance, celiac disease), not for “choosing the perfect diet”.
A practical minimum
- Fiber first (vegetables, legumes, whole grains) and enough protein, then everything else.
- If you are interested in personalization, choose a service that explains its method and publishes research, not one that only shows attractive scores.
- Judge results not by weekly weight but by markers over several months: blood pressure, HbA1c, lipids, how you feel.
