Top Ten Problems With Applying The Paleolithic Diet Principles: Number 9

9. Eating too much fruit

Due to unwarranted fears of saturated fats, and unwarrant beliefs in the healthfulness of fruit, would-be paleo dieters may replace the agricultural carbohydrates (cereals, legumes, etc.) with fruits. They may take a lead from Katherine Milton, Ph.D., who has proposed that high fruit consumption promoted human brain evolution and thus that fruit formed the main food in human ancestral Paleolithic diets.

This hypothesis has many counts against it, among which is evidence that humans do not have dental enamel well adapted to high consumption of the acids present in fruit. Grobler et al showed that just 6 minutes of exposure to fruit acids in the form of whole fruit caused enamel erosion on human teeth. West et al showed that orange juice erodes dental enamel in humans. Kunzel et al showed a positive correlation between degree of dental erosion and proximity to citrus plantations in Cuban children.

Cordain et al reported that among the Aussie Aborigines fruit appears to have supplied the bulk of energy from plant foods consumed. This supports optimal foraging theory, which indicates that animals including people will seek to get the maximum caloric return for foraging energy expenditures. Fruits are relatively easy to collect compared to digging up underground storage organs (USOs) like roots and tubers so we would predict foragers to prefer collecting fruits to digging up roots.

However, fruit did not supply the bulk of the total energy in their diet. Cordain (Table 1) reports that Aborigines obtained 77% of their total energy from animal food, only 23% from plant foods. About 41% of the plant food energy in Aborigine diets came from fruits, which means only about 9% of total energy in Aborigine diets came from fruit. Assuming a 2000 kcal diet, this would mean about 180 kcal from fruit daily, or about two pieces of modern fruit amounting to ~45 g carbohydrate.

Most of the wild fruits eaten by most hunter-gatherers did not provide the abundance of sugar supplied by modern hybridized fruits. Modern fruits supply large amounts of fructose, which Stanhope and Havel report can cause dyslipidemia, insulin resistance and hyperinsulinemia, which perpetuate a metabolic state dependent on sugars.

So it appears humans do not have a high tolerance or adaptation to diets containing large amounts of fruit. This again indicates that humans adapted to a diet built on fat and protein from hunted animals. A successful modern version of the paleodiet should put fruit in a minor, supporting role.