A new peer-reviewed study was published that examined the effects of keto and paleo diets on health and the environment. It’s not good news for followers of these diets.
There has been a lot written about the health effects of the keto or paleo diets, including the fact that they may not actually have much effect on weight loss, but many have wondered about their effect on the environment. This new research looks into the environmental effects of a keto diet, and it should be another good reason to find another way to lose weight.
Like I always do, let’s take a look at this new research and find out if it has anything to say about the effects of the keto diet on health and the environment.
What is the ketogenic diet?
The ketogenic diet, sometimes called the keto diet, is a diet that is high levels of fats, moderate levels of protein, and extremely low levels of carbohydrates. Interestingly, it was originally developed not as a means of weight loss, but to treat epilepsy. It eventually was replaced by much more effective methods such as anti-convulsant medications.
The premise of the weight-loss ketogenic diet is that if the body is deprived of glucose obtained from carbohydrate foods, it will produce energy from stored fat, which is biologically plausible. A typical version of this diet for adults has about 50% of the food by weight coming from fat (70% of calories).
In 2021, the American Heart Association issued a scientific statement of guidance for diets that improve cardiovascular health. They stated that:
…there is insufficient evidence to support any existing popular or fad diets such as the ketogenic diet and intermittent fasting to promote heart health.
It appears that for the past few years, science is not supporting the efficacy of the ketogenic diet for weight loss or heart health. Now, if there was good evidence that the diet did reduce weight over a long period of time, that would incidentally improve cardiovascular health. Since long-term weight loss has not been observed, the quality of the diet itself has a negative impact on cardiovascular outcomes.
Closely related to the keto diet is the paleolithic, or paleo, diet, which is based on the supposed ancient human diet of wild plants and animals that various hominid species habitually consumed during the Paleolithic era. It has become one of the more popular diet fads of the past few years.
The paleo diet consists mainly of fish, grass-fed pasture-raised meats, vegetables, fruit, fungi, roots, and nuts, and excludes grains, legumes, dairy products, salt, refined sugar, and processed oils. It really attempts to be scientific, but it seems to border on the edge of pseudoscience and can be considered a vogue diet, without much science backing it. Maybe it’s a good diet for health (we have no real evidence supporting it), but there is not any good scientific evidence that our paleolithic ancestors actually ate a paleolithic diet.
Even though there are slight differences between the diets, their outcomes for health and the environment are very similar.
The keto/paleo diets and environment paper
In an article published on 20 February 2023 in the American Journal of Clinical Nutrition by Diego Rose, Ph.D., MPH, RD, nutrition program director, Tulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana, and colleagues, examined the environmental and health impact of diets as consumed by US adults. The researchers examined a nationally representative survey of the 1-day eating habits of more than 16,000 individuals.
The data, which was captured by trained interviewers using a validated tool, categorized the participants into one of six mutually exclusive categories:
- Vegan — a strict vegetarian diet that does not include any meat product.
- Vegetarian — a diet that abstains from the consumption of any meat product, including red meat, poultry, fish, insects, or the flesh of any animal. There are variations of a vegetarian diet that may include animal products that are not the byproduct of slaughter, including eggs.
- Pescatarian — a mainly vegetarian diet that includes seafood.
- Keto — see the previous section.
- Paleo — see the previous section.
- Omnivore — the most common diet of humans and many primates, which resulted from millions of years of evolution. It includes plant and animal food sources.
The researchers examined the diet preferences of 16,412 individuals who were included in the analysis. Over 52% of the participants were female.
The environmental impact of the diets was calculated by matching the established greenhouse gas emissions (GHGE) of over 300 commodities to foods listed on the National Health and Nutrition Examination Survey (NHANES), which was then summarized for each individual to give a carbon footprint for their 1-day diet.
The quality of their diet was estimated using the 2010 versions of the Healthy Eating Index and the Alternate Healthy Eating Index, both of which award a score to food components based on their impact on health.
The researchers published the following results:
- The most common diet was an omnivore, which was followed by 83.6% of participants, followed by vegetarian (7.5%), pescatarian (4.7%), vegan (0.7%), keto (0.4%), and paleo diets (0.3%).
- The lowest carbon footprint, as measured by GHGE, was observed with the vegan diet, at an average of 0.69 kg of carbon dioxide equivalents per 1000 kcal consumed, followed by a vegetarian diet (1.16 kg of carbon dioxide equivalents per 1000 kcal) and pescatarian diet (1.66 kg of carbon dioxide equivalents per 1000 kcal). These were significantly lower than the other diets.
- The highest carbon footprints were observed with the omnivore (2.23 kg of carbon dioxide equivalents per 1000 kcal), paleo (2.62 kg of carbon dioxide equivalents per 1000 kcal), and keto diets (2.91 kg of carbon dioxide equivalents per 1000 kcal).
- In order of diet quality, the pescatarian diet was ranked the highest on both eating index scores mentioned above, followed by the vegetarian and vegan diets. Next was the omnivore diet, followed by either the paleo or keto diets, depending on which index was used.
- Finally, a further analysis of individuals following an omnivore diet suggested that those individuals who followed a DASH or Mediterranean diet had higher diet quality, according to the indices, along with a lower environmental impact, compared to others who followed an omnivore diet.
Summary of paleo/keto diets on the environment and health
Like I always write when reviewing these types of articles, I need to give caveats to the science here.
First, the diets were based on a one-day survey. Yes, that could mean someone appeared to be vegetarian for that one day but are truly an omnivore. However, the researchers included over 16,000 participants, so that error would be negated by the large numbers. In other words, with enough participants, someone following a vegetarian (or other) type of diet would show up more often in such a large survey.
Second, the diet is based on a questionnaire. Individuals might exaggerate what type of diet they’re using, though again, with so many participants that error would be lessened.
Third, the GHGE and diet quality are based on other surveys, which could allow for errors to creep into the analysis. However, the statistical analysis showed a difference between the diets for both diet quality and GHGE.
I think this study gets four out of five stars because the population size of participants plus the indices used for both environmental impact and diet quality are respected in scientific analyses.
And once more, the Mediterranean diet shows not only high diet quality but also improved environmental impact compared to the most common diet, omnivore. And it also shows that the keto and paleo diets are bad for the environment and bad for your health. I wish those diets would go away, but they’re going to make a whole team of cardiologists and oncologists very happy.
- Chiuve SE, Fung TT, Rimm EB, Hu FB, McCullough ML, Wang M, Stampfer MJ, Willett WC. Alternative dietary indices both strongly predict risk of chronic disease. J Nutr. 2012 Jun;142(6):1009-18. doi: 10.3945/jn.111.157222. Epub 2012 Apr 18. PMID: 22513989; PMCID: PMC3738221.
- O’Malley K, Willits-Smith A, Rose D. Popular diets as selected by adults in the United States show wide variation in carbon footprints and diet quality. Am J Clin Nutr. 2023 Feb 20:S0002-9165(23)00511-7. doi: 10.1016/j.ajcnut.2023.01.009. Epub ahead of print. PMID: 36868999.
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