I didn't watch the video, but read the article summary. Their approach - particularly to "low carb" dieting - was extremely problematic.
From the article:"I went on a no-carbohydrate diet - essentially no sugar - and Chris went on an extremely low-fat diet.
We were allowed to eat as much as we wanted, except I couldn't have carbohydrates and Chris was allowed only the barest amount of fat . . . .
Let me tell you straight up that both of these diets were miserable. I thought I'd got the better deal: I could eat meat, fish, eggs and cheese. But take away carbohydrates and the joy goes out of meals. And remove all fruit and veg - they all have carbs - and you get constipated. Though I was never hungry, I felt slow and tired, and my breath was terrible. . . .
One of the words you hear a lot when people talk about very low-carb diets is ketosis. This is where your body makes chemicals called ketones, which can act as fuel for the brain, which can't use fat. But they're not great brain food. While I wasn't distracted by hunger for the month, I felt thick-headed, and this was most evident in a stock trading competition with Chris. . . . The same was true for my physical performance. . . . Again Chris thrashed me in every test. So, even though I seemed to be losing more weight, everything became harder to do."
First of all, no carbs is unrealistic, and unnecessary. You can have some carbs and stay in nutritional ketosis - I try to stay at 15 net carbs per meal (carbs minus indigestible fiber), and I have stayed in ketosis for a long time now.
Second, carb content of vegetables varies drastically. I eat tons of leafy green vegetables and a really good amount of cruciferous vegetables, like broccoli and brussels sprouts. Along with lots of good fats like olive oil, high oleic sunflower oil and avocados, and moderate amounts of nuts, lean meats and fish. The folks who go straight to all steak and bacon are of course going to feel like shit.
Which brings me to my third point. The brain functions just fine on ketones - many folks report a much greater clarity and sense of awareness. But there is an adaptation period, commonly known as the "keto flu." It takes 2 weeks to a month to become keto-adapted, at which point the flu lifts. This informal experiment - like many formal experiments people have relied on to criticize low carb diets - shut off just at about the time when the subject should have started to feel better.
Fourth, because he wan't keto adapted, he wasn't getting the benefit of low carb dieting in his workouts. It is true that relying on carbohydrate for fuel makes strength training a little easier, though one can weight train just fine in a ketogenic state. The real benefits are in endurance exercise. There is limited body capacity to store glycogen, which is why folks hit the wall or "bonk." In comparison, fats are an almost unlimited source of ketones, so keto-adapted endurance athletes can do great things.
In sum: There are benefits and drawbacks to each style of diet, but this "experiment" was a pile of shit.