Is there an optimal diet? Maybe not

The findings suggest there is no one "true" diet for humans, who "can be very healthy on a wide range of diets".
The findings suggest there is no one "true" diet for humans, who "can be very healthy on a wide range of diets".PHOTO: THE NEW PAPER

NEW YORK • What is for dinner tonight?

Nutrition experts have long debated whether there is an optimal diet, but a study published recently found that there is most likely no one natural diet that is best for human health.

The research, published in journal Obesity Reviews, viewed the diets, habits and physical activities of modern hunter-gatherer groups and small societies whose lifestyles are similar to those of ancient populations.

They found that they all exhibit generally excellent metabolic health while consuming a wide range of diets.

Some get up to 80 per cent of their calories from carbohydrates. Others eat mostly meat.

But there were some broad strokes. Almost all of them eat a mix of meat, fish and plants, consuming foods generally packed with nutrients.

In general, they eat a lot more fibre than the average American.

Most of their carbohydrates come from vegetables and starchy plants with a low glycaemic index. But it is also not uncommon for hunter-gatherers to eat sugar, consumed primarily in the form of honey.

The findings suggest there is no one "true" diet for humans, who "can be very healthy on a wide range of diets", said the study's lead author, associate professor of evolutionary anthropology Herman Pontzer at Duke University.

"We know that because we see a wide range of diets in these very healthy populations."

One thing hunter-gatherer populations have in common is a very high level of physical activity. Many walk between 8km and 16km a day.

Yet they do not have higher energy expenditure levels than the average American office worker. That suggests that the authorities should consider recommending exercise primarily as a way to improve metabolic health, but not necessarily as a calorie-burning antidote to obesity.

From a public health perspective, modern hunter-gatherers may be most remarkable for their relative lack of chronic diseases such as heart disease, hypertension and cancer.

Obesity rates are low. They have very high levels of cardio-respiratory fitness, even in old age. And Type 2 diabetes and metabolic dysfunction are hardly ever seen.

But life in hunter-gatherer societies is not easy. Infant mortality rates are high because of infectious disease. Deaths from accidents, gastrointestinal illness and acute infections are common.

Those who survive to adulthood often reach old age relatively free from degenerative diseases that are the norm in industrialised nations.

They are typically fit and active until the end, suggesting that there is something about their way of life that allows them to age healthfully.

"Few of us would want to trade places with them. Their lives are still tough," Prof Pontzer said.

 

"But the things they get sick from are things we know how to deal with, and the things they don't get sick from are the things we struggle to deal with."

It is possible that genetics and other factors unrelated to lifestyle protect them from chronic disease.

But studies show that when people born into hunter-gatherer societies move to large cities and adopt Western lifestyles, they develop high rates of obesity and metabolic disease just like everyone else.

Professor Michael Gurven, an anthropologist at the University of California, Santa Barbara, has done extensive research on the Tsimane, a Bolivian population that has a subsistence lifestyle of hunting, gathering, fishing and farming.

He has published studies showing that they have exceptional cardiovascular health and almost no diabetes.

Yet he has seen several cases of Tsimane people developing and dying from Type 2 diabetes after moving to the nearby town of San Borja, where they took sedentary office jobs and gave up their traditional diet.

For the new study, Prof Pontzer and his colleagues analysed data on hunter-gatherers and other small-scale societies, from South America to Africa to Australia.

They looked at detailed dietary assessments of fossil and archaeological records to get a sense of what early humans ate.

And they included new data collected from the Hadza, a community of people who spend their days hunting and foraging in Tanzania, much as their ancestors have for tens of thousands of years.

The amount of daily calories the Hadza consume is similar to that of the average American. But they rely on a fairly small number of foods.

Notably, they do not have potato chips, candy, ice cream and other processed foods that combine large amounts of fat and simple carbohydrates.

The lack of novelty and variety in hunter-gatherer diets may be part of the reason they do not overeat and become obese. Studies show, for example, that the greater the variety of food choices, the longer it takes to feel full, a phenomenon known as sensory specific satiety.

Prof Pontzer said: "It's the reason you always have room for dessert at a restaurant even when you're full.

"Even though you've had a savoury meal and you can't eat one more bite of steak, you're still interested in the cheesecake because it's sweet and that button hasn't been worn out in your brain yet."

NYTIMES

A version of this article appeared in the print edition of The Straits Times on December 31, 2018, with the headline 'Is there an optimal diet? Maybe not'. Print Edition | Subscribe