The digestive abilities of anatomically modern humans, however, are different from those of Paleolithic humans, which undermines the diet's core premise. During the 2.6 million year-long Paleolithic era, the highly variable climate and worldwide spread of human populations meant that humans were, by necessity, nutritionally adaptable. Supporters of the diet mistakenly presuppose that human digestion has remained essentially unchanged over time.
To get an idea of what that means, we turned to the experts, including Loren Cordain, PhD, a professor emeritus at Colorado State University in Fort Collins, Colorado, and the author of The Paleo Diet; Erin Holley, RD, of Ohio State University Wexner Medical Center in Columbus, Ohio; and Lona Sandon, PhD, RD, an assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center in Dallas.
Trying to devise an ideal diet by studying contemporary hunter-gatherers is difficult because of the great disparities that exist; for example, the animal-derived calorie percentage ranges from 25% for the Gwi people of southern Africa to 99% for the Alaskan Nunamiut. Descendants of populations with different diets have different genetic adaptations to those diets, such as the ability to digest sugars from starchy foods. Modern hunter-gatherers tend to exercise considerably more than modern office workers, protecting them from heart disease and diabetes, though highly processed modern foods also contribute to diabetes when those populations move into cities.
Some CrossFitters drink WAYYY too much “kool-aid.” You’ll run into CrossFit people who think CrossFit is the be-all, end-all training solution, and anybody that doesn’t do CrossFit is a wuss. If you can do 20 pull ups, they can do 22, and do them faster than you, after doing 25 handstand push ups and running 400 meters. I tend to dislike elitists no matter what they are elitist about, and CrossFit is no exception.
LOREN CORDAIN, Ph.D., is one of the top global researchers in the area of evolutionary medicine. Generally acknowledged as the world's leading expert on the Paleolithic diet, he is a professor in the Health and Exercise Science Department at Colorado State University. Dr. Cordain and his research have been featured on Dateline NBC and in the New York Times, the Wall Street Journal, and other media. He is the author of The Paleo Diet and The Paleo Diet Cookbook, among other books, and makes regular media and speaking appearances worldwide.
The Paleo Diet focuses on foods that are high in protein, low in carbs, and rich with fiber. There's a strong emphasis on meat, fruits, and vegetables — basically, anything our ancestors would have consumed more than 10,000 years ago during the Paleolithic era. (There's actually some truth to this: in July 2018, when researchers identified the stomach contents of the 5,300-year-old mummy Otzi, they found that his last meal was high-fat and contained "animal and plant remains," making it pretty Paleo-friendly.)
Excluding foods. The exclusion of entire categories of commonly eaten foods like whole grains and dairy requires frequent label reading in the supermarket and in restaurants. It may also increase the risk of deficiencies such as calcium, vitamin D, and B vitamins, if these nutrients are not consistently eaten from the allowed foods or a vitamin supplement. For example, there are some nondairy calcium-rich foods that are absorbed well by the body such as collard and turnip greens or canned bone-in sardines and salmon, but you would have to eat five or more servings of these greens and fish bones daily to meet recommended calcium needs. (Note that some greens like spinach that are touted to be calcium-rich also contain oxalates and phytates that bind to calcium so very little is actually absorbed.) One small, short-term intervention study of healthy participants showed a 53% decrease from baseline in calcium intake after following a Paleo diet for three weeks.  Furthermore, the exclusion of whole grains can result in reduced consumption of beneficial nutrients such as fiber and thus may increase one’s risk for diabetes and heart disease.
The NY Times had a blog article on Good News on Saturated Fat which is reporting on Gary Taubes's interpretation of the new report in The New England Journal of Medicine on a two-year diet experiment in Israel. A followup is the post The Fat Fight Goes On where Gary rebuts the arguments against the study. And here's a good interview with Taubes (and includes a good summary): Gary Taubes on Cold Fusion, Good Nutrition and What Makes Bad (and Good) Science.
My fiancee and I did this together. It takes teamwork (if you have a family, you probably need to get them on board). It also will help if you can begin (or even complete) this diet when you have a minimum of social obligations--having office mates who eat a lot of cake or friends who drink a lot of booze WILL NOT HELP while you are on this program. Don't try to start this the week before Christmas if your family gathers to eat until they pass out. Be realistic about when you begin this. You must prepare a little bit and read the book ahead of time so you aren't just floating at sea. And, be aware: you will not be able to sufficiently screen foods made by other people!
In response to these criticisms, CrossFit, Inc. claims, “CrossFit is relatively safe even when performed with poor technique, but it is safer and more effective when performed with good technique.” CrossFit, Inc. also claims risk for injury can be reduced by properly scaling and modifying workouts, a concept taught on its website and at the CrossFit Level 1 Trainer Course.
This list is going to be a little longer than the last. You cut out all sugar (both real and all substitutes whether natural or artificial, like honey, maple syrup, Splenda, etc.). No grains, legumes (including all forms of soy), dairy, or alcohol. You’re also told to avoid additives like MSG and carrageenan, although that should happen naturally if you’re sticking to whole foods.
ICYMI: Whole30 is an elimination-style diet that asks dieters to ban all soy, dairy, grains, alcohol, legumes, and added sugars from their diet for 30 days straight. The point is to flush your system, so when the 30 days are up, you can slowly add different food groups back and get a sense of which ones have been secretly affecting your physical and mental health. The creator, Melissa Hartwig, also says Whole30 will change your entire relationship with food.
Eat low to moderate amounts of fruits and nuts. Try to eat mostly fruits low in sugar and high in antioxidants like berries as well as nuts high in omega-3, low in omega-6 and low in total polyunsaturated fat like macadamia nuts. Consider cutting off fruits and nuts altogether if you have an autoimmune disease, digestive problems or are trying to lose weight faster.
That's a lot of tension--doing everything possible to make CrossFit a mainstream sport while legally or digitally body slamming anyone who refers to the CrossFit name to cater to its athletes or fans. Glassman has always thrived on doing the opposite of what anyone has ever figured was sensible or possible. But now Glassman's own intentions, of doing what he wants and letting others do what they want, are pressing up against each other more every day. In CrossFit, Glassman is hoisting two massive, contending ideas at once: CrossFit is an open-source workout for everyone to enjoy; CrossFit is a trademarked brand protected as viciously as a Hells Angels jacket. If it comes clattering down, it will be painful as all hell to watch. But if it succeeds? It won't be the first time a CrossFitter shocks people with how much weight he put above his head. You can bet Glassman's gonna try for another rep.