How sustainable are the keto and paleo diets?

Food is one of the most direct ways in which we connect to nature. Even the most urban dwelling person eating a processed diet eats what comes from nature. 

Food choices also affect nature. Food production is intimately intertwined with the environment and with our climate, especially with the exponential growth of the human population and our expanding consumption patterns.

And food choices matter: Our diet affects our own health, and also the health of our planet, as the carbon footprint of different food choices carries different environmental costs. 

The American diet changes over time, and as people aspire to improve their health and weight status they’re open to hearing about new eating patterns – and their environmental impact. On the rise are the Mediterranean style diet and several plant forward ones, and the paleo and keto diet are also gaining a following – it’s estimated that ~10 percent of Americans are giving them a try. A new study in the American Journal of Clinical Nutrition looks at the carbon footprint of these and other popular diets.

The study includes more than 16,000 people whose diet was categorized into vegan, vegetarian, pescatarian, paleo, keto, or omnivore – which includes all other diets. The carbon footprint of each dietary pattern was calculated using a previously developed database of food impacts on the environment called dataFIELD. The diet quality of each diet was assessed by comparing it to the Healthy Eating Index (HEI) and the Alternate Healthy Eating Index (AHEI). 

And the results: Keto and paleo diets have a higher carbon footprint and a lower mean diet quality than vegetarian, vegan, and pescatarian diets. The keto diet, which is a high-fat low-carb diet, is estimated to produce almost 3 kg of carbon dioxide for every 1,000 calories of food. The paleo diet, which prioritizes meats, nuts and vegetables, emits 2.6 kg of carbon dioxide for every 1,000 calories. A vegan diet, on the other hand,  generates 0.7 kg of carbon dioxide per 1,000 calories – less than a fourth of a keto diet.

How much difference could changing your diet make? “For any given day, if a third of the omnivores consumed a 2000 kcal vegetarian diet, and assuming accompanying shifts in domestic production, the savings would be equivalent to eliminating 340 million passenger vehicle miles,” the authors write. Over a year this would amount to about 5 percent of what we needed to do to meet the US targets of the Paris accords, and improve our diet quality, reducing risk of chronic disease.

An omnivore’s compromise

The single most environmentally-impactful food choice regards animal products. Animal food production emits much more greenhouse gasses than plant foods. Beef production emits 10 times more than chicken, and 20 times as much as growing legumes, nuts and seeds. 

Studies show that vegan and vegetarian diets emit less greenhouse gasses. Several other diets that are usually adopted for health benefits – such as the Mediterranean-style diet and the DASH diet also carry a smaller carbon footprint than the typical American diet.

We can all take steps towards greater sustainability by eating more plants and less meat, eating less processed foods, choosing organic when possible, preferring produce that's locally grown and in season, and avoiding waste.

Even the smallest steps count in a world with more eight billion people making food choices.

Dr. Ayala