In this new study, researchers put 44 healthy men and women (age: early 30s) on an unrestricted Paleo diet for 10 weeks. The diet included lean meat, fish, eggs, nuts, fruit, and vegetables. No grains, beans, or dairy. No processed food, sugar, soda, or coffee. It is meant to mimic perceived food consumption of humans during the Paleolithic Era, a time before cultivation and domestication of animals. Participants also engaged in a CrossFit-based, high-intensity circuit training program:
Unrestricted Paleolithic Diet Is Associated With Unfavorable Changes To Blood Lipids In Healthy Subjects, International Journal of Exercise Science, 15 February 2014
After 10 weeks, cholesterol measurements worsened:
HDL (baseline optimal): Pre 82, Post 68
LDL: Pre 93, Post 106
Total Cholesterol (TC): Pre 169, Post 179
TC/HDL, Pre 3.0, Post 3.3
HDL is “good” cholesterol. You want it to go up. It went down. LDL is “bad” cholesterol. You want it to go down. It went up. These changes reached a level of statistical significance (so, not due to chance) and were, to use the authors’ term, “substantial.”
Triglycerides also increased slightly. The worst outcomes were seen among the subgroup that had been the healthiest before starting the diet.
“Subjects with optimal initial blood lipids were unable to maintain their ideal blood lipid values after adhering to the Paleo diet for 10 weeks.”
Interestingly, subjects also decreased body weight (about 7 pounds) and body fat (from 24.3% to 20.7%), two changes that are often accompanied by improvements in cholesterol levels, not detriments.
“Our results demonstrate that an ad libitum unrestricted Paleo diet intervention is associated with deleterious changes to blood lipids in healthy subjects, despite concurrent improvements in body composition and cardiorespiratory fitness.”
You may exercise and appear fit, but what you eat matters. This reminds me of the runners who develop atherosclerosis and die prematurely. Being lean, muscular, and aerobically fit may not be enough to counteract effects of a poor diet.