Still, many scientists have expressed concern that we do not yet have enough evidence to make any strong claims about the paleo diet’s health benefits, especially its long-term effects. In fact, in an article in response to the first review, authors Tanis R. Fenton and Carol J. Fenton, from the Cumming School of Medicine in Canada, wrote a letter to the editor in which they expressed their disappointment with the review. (5)
Grass-fed beef is often highlighted on the diet, which is promoted to contain more omega-3 fats than conventional beef (due to being fed grass instead of grain). It does contain small amounts of alpha-linolenic acid (ALA), a precursor to EPA and DHA. However, only a small proportion of ALA can be converted in the body to long-chain omega-3 fatty acids (EPA and DHA). The amount of omega-3 is also highly variable depending on the exact feeding regimen and differences in fat metabolism among cattle breeds.  In general, the amount of omega-3 in grass-fed beef is much lower than that in oily marine fish.  Cooked salmon contains 1000-2000 mg of EPA/DHA per 3-ounce portion, whereas 3 ounces of grass-fed beef contains about 20-200 mg of ALA.
A metaresearch group at Tilburg University in the Netherlands investigates scientists’ research methods and operations, scrutinizing questionable practices such as selective reporting of statistical tests and data massaging. The group instead advocates for practices such as preregistering studies and making experimental data immediately available for open external review and verification. Its members are optimistic that “the perverse incentives of careerist academia, to hoard data and sacrifice rigor for headline-generating findings, will ultimately be fixed.”