The obesity epidemic is often blamed on “thrifty genes.” According to this theory, we evolved in a food-scarce environment. When food was actually plentiful, the theory goes, it paid to eat as much as possible, and gain lots of fat.
This fat allegedly helped save us during future famines—famines which no longer come.
Hence, modern obesity.
This theory is often presented as if it were a fact.
But the thrifty-gene hypothesis is directly contradicted by the people of Kitava. The Kitavans are a Melanesian island people who were studied by a team of researchers in the early 1990s. At the time, the Kitavan population numbered about 2300 people.
Interestingly, in this entire population, obesity was nonexistent. No one was fat. Instead, the Kitavans were quite skinny, with average middle-aged BMIs of 18 for women, and 20 for men.624
(“Overweight” is 25+.)
What did the Kitavans eat? Their diet mostly consisted of fruit and root vegetables.
And here’s the thing. According to Staffan Lindeberg, MD, PhD, the lead scientist studying the Kitavans:
It is obvious from our investigations that lack of food is an unknown concept, and that the surplus of fruits and vegetables regularly rots or is eaten by dogs.625
The Kitavans, then, had plenty of food. They didn’t live in food scarcity. They didn’t endure periodic famines that kept them lean. They regularly threw food away.
Nor were the Kitavans terribly active. Based on their average daily calorie expenditure (which was 1.7 times their basal metabolic rate) the Kitvans only fell into the “moderately active” category.626
So the Kitavans were neither short on food nor long on exercise.
And none of them were fat.
The reason the Kitavans were skinny and we are fat wasn’t due to food quantity, as the thrifty-gene hypothesis suggests.
The Kitavans had all the fruit and root vegetables they wanted.
We have all the processed food we want.
What causes obesity isn’t food quantity, but food quality.
It’s commonly thought that hunter-gatherers—and by extension, early humans—are in a constant struggle to get enough food. Hunter-gatherers are often depicted as running around all day like chickens with their heads cut off in a desperate and nearly futile attempt to find enough calories to stay alive.
But despite this widespread and rather grim belief, evidence indicates that hunter-gatherers don’t actually experience more food shortages than agriculturalists.627
They generally have enough to eat.
And critically, this goes for modern hunter-gatherers, who have been relegated to marginal environments by encroaching civilization.
Ancient hunter-gatherers—the ones that helped shape our genes—likely enjoyed much more food-rich and bountiful environments than their modern kin.
Nevertheless, modern hunter-gatherers only spend about two to three hours a day actively procuring food.628
For them, getting enough to eat is only a part-time job.
(And as we saw with the Hadza, hunter-gatherers don’t necessarily burn more calories than we do, in absolute terms, because we burn more calories at rest.629)
But most egregiously, perhaps, the thrifty-gene hypothesis sells ancient humans short. In our evolutionary niche, we were apex predators who could make flint-tipped spears, control fire, and were equally capable of subsisting on plants.
We were one of the smartest species alive, with profound environmental knowledge accumulated over hundreds of generations, and much of our collective brainpower devoted to figuring out the most efficient ways to hunt and gather.
Getting enough food was unlikely to have been a regular problem.
A Theory Unraveled
The thrifty-gene hypothesis completely fails to explain the recent obesity explosion. Widespread obesity really only took off in the late 1970s.630 But in countries like the United States, it’s not like food was scarce in the 1950s and 1960s.
If our genes were really so thrifty, obesity should have exploded as soon as the Industrial Revolution stabilized national food supplies, which happened long before the 1970s.
On a more basic biological level, the thrifty-gene hypothesis is simply implausible. It isn’t plausible that humans and other species wouldn’t have an innate weight-regulating mechanism to keep their weights in a stable range when food was plentiful.
A species that stuffed itself until it got fat and slow at the first sign of surplus would have been at a major evolutionary disadvantage to one that maintained a lean and healthy weight during times of plenty—and would have gone extinct.
Eat Until You’re Full
To purposely eat less than you want is dreary and unnatural. Eating until you’re full is a far more enjoyable, practical, and sustainable way to go through life.
One of the core premises of this book is that if you’re eating whole foods, you can eat until you’re full, and lose weight.
(Or at the very least, stop gaining weight.)
It’s not food abundance, but processed-food abundance that throws a wrench in our weight-regulating mechanism and makes us fat.
As we’ll see, you can eat just about any whole food with impunity.
624. Lindeberg et al., “Age Relations of Cardiovascular Risk Factors in a Traditional Melanesian Society: The Kitava Study,” American Journal of Clinical Nutrition 66, no. 4 (1997): 845-852.
625. Lindeberg, Staffan. Food and Western Disease: Health and Nutrition from an Evolutionary Perspective. Hoboken: Wiley-Blackwell, 2010. Kindle File, Chapter 4.5, Location 3081 of 11554.
626. Ibid., Chapter 4.1, Location 2319 of 11554.
627. Benyshek D., and Watson, J., “Exploring the Thrifty Genotype’s Food-Shortage Assumptions: A Cross-Cultural Comparison of Ethnographic Accounts of Food Security Among Foraging and Agricultural Societies,” American Journal of Physical Anthropology 131, no. 1 (2006): 120-6.
628. Lindeberg, Staffan. Food and Western Disease: Health and Nutrition from an Evolutionary Perspective. Hoboken: Wiley-Blackwell, 2010. Kindle File, Chapter 4.6, Location 3474.
629. Pontzer et al., “Hunter-Gatherer Energetics and Human Obesity,” PLOS One 7 (2012): e40503. doi:10.1371/journal.pone.0040503
630. Ogden et al., “NCHS Health E-Stat: Prevalence of Overweight, Obesity, and Extreme Obesity Among Adults: United States, Trends 1960-1962 through 2007-2008,” Centers for Disease Control and Prevention, Publications and Information Products. https://www.cdc.gov/nchs/data/hestat/obesity_adult_07_08/obesity_adult_07_0