Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

New Research Indicates Paleo Diet Isn’t Good for Your Heart

Dear Doctor: I’ve been doing paleo for a month, and I have lost 12 pounds. Now my mom is talking about a new study that says the diet is not good for your heart. Can you explain? Do you think it’s the same for keto?

Dear Reader: You’re referring to two popular approaches to weight loss that have captured the attention of many dieters. For those who may not be familiar with these eating plans, both entail limiting carbohydrate intake in some way. They also include a focus on proteins -- typically poultry, meat, fish and eggs -- as well as fats.

The paleo diet -- that’s short for Paleolithic -- relies on the nutrients that would have been available to our ancient ancestors through hunting and gathering during the Old Stone Age era. It eliminates foods obtained by farming and herding, such as legumes, grains and dairy products. The diet dates back to the 1970s, but it boomed in popularity beginning in 2002 after the publication of a paleo diet book. The paleo diet includes lean meats and fish, and limited amounts of certain fruits, vegetables, nuts and seeds.

The ketogenic diet, shortened to keto, was developed in the 1920s to manage some kinds of epilepsy. It recommends that fats account for 55% to 60% of daily nutrient intake, and that carbs make up no more than 10% of the daily diet. This leaves the remaining 30% to 35% of calories for protein.

Both diets trigger a metabolic process known as ketosis, which occurs in the absence of adequate carbohydrates, the body’s go-to energy source. It’s a lot more complex than we have time for in this column, but the bottom line is that when in ketosis, the body burns stored fat for energy.

Due to widespread interest in paleo and keto diets, and because each restricts various foods with essential nutrients, including vitamins, minerals, micronutrients and fiber, researchers are taking a closer look. Your mother is referring to a study published last summer in the European Journal of Nutrition. Scientists monitored the gut microbiomes of 45 people following the paleo diet, and compared them to a control group eating a balanced diet. After one year, the paleo group had significantly higher levels of a molecule known as TMAO (for fellow science nerds, that’s trimethylamine N-oxide), a marker associated with heart disease. The diversity of the gut microbiomes of the paleo group was also adversely affected.

Given the restrictive nature of these diets, as well as their high levels of meat and saturated fats, the results of the study are not surprising. This particular research didn’t look at the keto diet, but other studies have pointed to similar long-term health risks. In the short-term, however, we think low- and no-carb diets can be useful tools. We have seen this among our own patients, who use a low-carb approach to jump-start weight loss. We recommend that they minimize animal and saturated fats and instead focus on lean meats, seafood and plant-based fats, and then gradually transition to a well-rounded and sustainable diet.

(Send your questions to, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)