Although mammals thrive on similar
macronutrient ratios, we can tease out a
few differences among omnivore,
herbivore, and carnivore diets.
Each diet has a different strategy for
meeting the body’s glucose needs:
• Omnivores eat enough
carbohydrates to meet the body’s
glucose needs directly.
• Herbivores obtain little glucose
from their diet but up to 70
percent of their energy needs
from short-chain carbon atoms
produced by bacterial
fermentation. Short-chain fatty
acids with even numbers of
carbon atoms may be
transformed in the liver into
ketones, which nourish neurons,
reducing the body’s glucose
needs; fatty acids with odd
numbers of carbons may be used
to manufacture glucose.
• Carnivores obtain few or no
carbohydrates from their diet and
meet their glucose needs by
manufacturing glucose from
protein.
The fact that these three strategies are
all evolutionarily successful shows that
they can all produce superb health in
mammals. There are some implications
for human diets:
• Most mammals satisfy their
glucose needs by
manufacturing glucose in the
liver, not by eating it. This
suggests there may be a health
advantage to keeping glucose
intake a little below the body’s
needs and thereby keeping blood
glucose levels low. This is a
clue to the benefits of low-carb
diets.
• Mammalian short- and
medium-chain fat intakes cover
a huge range—0 to 70 percent.
This tells us that short- and
medium-chain fats are safe for
humans and that ketogenic diets,
in which a large share of
calories is obtained from shortand
medium-chain fats—for
instance, diets with a very high
intake of coconut oil, which is 58
percent medium-chain fat—may
be a feasible human dietary
strategy. This is good because
ketogenic diets are therapeutic
for some diseases.
We think it’s fair to say that the
solution to the optimal human diet was
there all along—in the zoo! Mammalian
diets are a reliable guide to the nutrient
needs of the body and therefore to what
we should be eating.
