What a 1971 fruit-heavy diet trial found about glucose and blood lipids
A 1971 South African study examined biochemical responses to a mainly fruit diet supplemented with nuts. Its findings on glucose, insulin and blood lipids provide historical context for research on fruit-rich dietary patterns.
What the study did and found
B. J. Meyer and colleagues investigated volunteers consuming a fruit-centered diet supplemented with nuts. Participants included nine Black South African male hospital patients, eight White volunteers completing the intervention and one woman already following a similar diet.
Glucose tolerance tests showed increased fasting glucose in the Black group without significant overall deterioration in glucose tolerance. Insulin responses declined significantly in most Black participants but not consistently in the White group.
Total plasma lipids decreased significantly in both intervention groups after 12 weeks. Cholesterol, triglycerides and phospholipids also declined in certain groups or measurement periods. Plasma-protein changes included increased albumin in the Black group.
The authors considered the diet adequate for the biochemical parameters examined but cautioned that responses could vary with dietary composition, duration and individual circumstances.
Why it is cited
The study remains notable as an early human intervention examining unusually high fruit consumption. A 2018 randomized trial cited it when discussing fruit-rich diets, fructose, uric acid and blood pressure.
However, the intervention included nuts, substantial avocado consumption and some other foods. Its findings therefore cannot be attributed exclusively to fruit.
Modern research generally examines whole fruit within broader dietary patterns rather than predominantly fruit-based regimens. Reviews published in 2021 and 2025 associated greater fruit consumption with potentially favorable cardiometabolic outcomes, although evidence quality varied.
The 1971 experiment involved small, distinct participant groups, multiple simultaneous dietary changes and biochemical measurements rather than long-term clinical outcomes. Its findings cannot establish the long-term safety, nutritional completeness or superiority of fruit-dominant diets.
The topic today
WHO's 2026 healthy-diet guidance emphasizes dietary diversity, nutritional adequacy and at least 400 g of fruits and vegetables daily for people older than 10 years.
Contemporary research distinguishes whole fruit from juice and examines fibre, dietary substitutions and long-term metabolic outcomes. The 1971 study remains a historical contribution to understanding biochemical responses to fruit-rich diets, not evidence supporting an exclusively or predominantly fruit-based diet as a universal recommendation.