Anyone who is a regular reader of this blog will have noticed that the last post on intermittent fasting generated an enormous number of comments, just about all of which I tried to answer. Most of these comments were questions about intermittent fasting or people giving their dietary histories or people informing us that they were starting an intermittent fast. Other comments asked for answers to specific medical questions while others wanted to know if MD and I had abandoned the low-carb diet in favor of intermittent fasting. I figured that this would be a good time to set the record straight.

MD and I feel strongly that we as a species have a genome that was molded by the forces of natural selection over the past few million years to operate optimally on the food that was at hand during those few million years. What was available? Mainly fairly high-protein, high-fat fare. There weren’t a lot of carbohydrates readily available until the advent of agriculture a few thousand years ago. For the time that we developed our ancestors ate meat, fish, insects, clams, reptiles and pretty much anything live they could get their hands on. This primarily protein and fat diet was supplemented with whatever fruits, nuts, berries, roots, shoots and tubers were in season. Work done by Loren Cordain shows that, based on the Ethnographic Atlas, modern day hunter gatherers get about 65 percent of their calories from animals and the other 35 percent from plants. Most researchers believe that Paleolithic man got more than that from animals because during Paleolithic times many more large animals roamed the earth than do today. In fact, Paleolithic man hunted many of these large animals to extinction.

It is pretty safe to say that the macronutrients that set our genome were fat and protein. Many unenlightened people seem to believe that early man lived in land of carbohydrate abundance, and, consequently, thrived on a high-carbohydrate diet. It can easily be seen that this wasn’t the case simply by calculating how much food would have to be consumed to get enough calories from the available plant sources.

Taking 3000 kcal as being the average (it’s probably on the low side) daily energy intake of our Paleolithic ancestors and looking at how much plant food would be required to obtain those kcal is an eye-opening experience. I ran just a few foods through the USDA nutritional calculator and found that it would take 48 cups of blackberries–that’s 3 gallons of blackberries–to provide 3000 kcal. I don’t know how many readers have ever picked blackberries, but I have, and I can tell you that picking 3 gallons takes a lot of time. And, much though I love blackberries, I couldn’t come anywhere near eating 3 gallons of them in a day. How about blueberries? 36 cups; over 2 gallons. Spinach? 103 cups. Celery? 111 stalks. Apples? 42.

It was only after the advent of agriculture that calorically dense carbohydrate foods came into existence and became the common fare for man. Until then, our ancestors, if they were to subsist on plant foods only, would have had a pretty rough time of it getting enough without eating all the time. Which is exactly what the mountain gorillas do. Although mountain gorillas have the same carnivore GI tract that we do, early in their evolution (probably lead by the gorilla version of Dean Ornish) they opted for vegetarianism. These animals eat constantly to get enough plant food to meet their energy needs. They take food to bed with them so it will be available when they first awaken. They roam through the jungle throughout the day eating non-stop except for brief rest periods.

Given the above facts, it’s pretty clear that early man ate a fair amount of meat. After all, it takes only a couple of 16 ounce fatty steaks to provide 3000 kcal, which is a whole lot easier to down than 3 gallons of blackberries. It would then stand to reason that as a species we would perform better on a meat, or at the very least, a higher protein, lower carb diet since that’s what we had to eat for a few million years. In one of my favorite quotes, Dr. Blake F. Donaldson, a crusty old physician from New York who wrote a book called Strong Medicine, says:

During the millions of years that our ancestors lived by hunting, every weakling who could not maintain perfect health on fresh fat meat and water was bred out.

When we saw patients in our clinic for obesity and the other so-called diseases of civilization, MD and I successfully treated them with diets that approximated what we–based on the anthropological evidence–believed early man ate. We basically gave them the food they were designed by nature to eat. Obviously we couldn’t have them eating fresh mastodon steaks or cave bear fillets, so we had them eat the modern day equivalent (or as equivalent as it could get in the modern day) that could be found at the grocery store or in restaurants. We had to develop a diet that was palatable, not overly difficult to obtain and prepare, and that would allow them to live their regular lives and go about their business. After refining and tweaking, the diet we came up with is what we described in the book Protein Power. We diddled with it a little more and added a few supplements and made some more lifestyle recommendation such as getting more sunshine and getting rid of excess iron that went along with our Paleolithic origins and published the Protein Power LifePlan.

Since that time we’ve continued to think about the optimal diet and experiment with different permutations of the Paleolithic diet. We still believe that a low-carbohydrate, higher-protein, higher-diet is the optimal one for humans. In thinking about how to make a low-carb diet better, it dawned on us that there is another factor besides the actual food eaten in any particular diet: the timing of the eating. We began to think about how often Paleolithic man ate. We looked at data from modern day hunters and found that most of them didn’t eat all that often, and that when they did eat, they gorged.

Once we decided that meal timing was probably important in the development of our genome just as was the kinds of foods consumed, we started looking for evidence in the medical literature. There we came upon the studies on intermittent fasting (IF).

I covered intermittent fasting at length in the previous post. I was amazed that whatever goes on during the fasting process is potent enough to overcome the health negating effects of ad lib feeding because the animals that were underwent the IF had the same health benefits as did those that were calorically restricted yet the IF animals ate the same as the (ultimately sickly) ad libitum fed animals. And the IF animals lived as long as the calorically restricted animals despite eating as much as the much less long-lived ad lib fed animals.

Clearly something powerful takes place during a fast. What is the mechanism? Who knows at this point. But it’s something that should inspire a battalion of researchers to get busy looking into.

Now, based on the IF research data, MD and I are of the opinion that a Protein Power style diet interspersed with a little fasting is probably the optimal diet. We ourselves follow this diet. We eat one meal a day sometimes, a couple of meals others, and sometimes three squares. If we’re not hungry we don’t eat. We try to fight off the culturally induced feelings of, Oh, it’s lunchtime, so I must we must be hungry: let’s eat.

We tried the IF as written up in the post because we wanted to see if there was a particular regimen we could give people wanting to try it out. We know from many years of taking care of people on diets, that dieters want rules. The more we would write our material in such a way as to give patients (and readers) a lot of lee way in how they could prepare their low-carb diets, the more calls we got from these patients asking for us just to give them a set of meal plans. We found that the IF was easiest for us with a 6 PM cutoff; that’s why I described it that way.

There is probably no magic in the 24 hours; who knows, maybe it’s 15 hours. It just isn’t known at this point. I’m firmly convinced, however, that there is an advantage to going without food for periods here and there. I’m convinced for a couple of reasons. First, all the data on IF is pretty persuasive. Second, all the Ornishes, Barnards, Grundys and the other AOE (Architects of the Obesity Epidemic) recommend that we all eat a lot of small meals throughout the day. Given the track records of these people alone, it militates that we should eat large meals separated by long periods of time.

We still fully believe in Protein Power. We haven’t abandoned it in favor of IF. We have added IF to our own lives from time to time, especially if we go off the Protein Power wagon. But, we also IF using strict Protein Power, too, In short, IF is just an adjunct to the Protein Power diet that makes it work better by making it even more like the Paleolithic diet we cut our collective teeth on.

Once again I have to reiterate that I can’t answer specific medical questions over the Internet. Unless you’re my patient (and by that I mean someone who I have examined) I can’t tell you why you’re having this reaction or that. If your ankles are swelling, I don’t know why unless I can take a medical history and examine you. If you’re exhausted on the IF or any other regimen, it could be that you need a little potassium, or it could be something else. Whatever it is, I can’t give you an answer unless I take a medical history and do an exam.

One final note:

One of the commenters on the IF post is Robb Wolf who has worked with Loren Cordain and is himself well read on the literature of IF. He sent me an interview with Dr. Thomas Seyfried on ketosis and cancer that he said I could share with my readers. (click Download file to download the PDF) In the interview Dr, Seyfried discussed IF and some of its therapeutic uses. (You can also click here to read Dr. Seyfried’s paper on ketosis and brain cancer published this year in Nutrition & Metabolism)

Robb is the Editor-in-chief of the publication Performance Menu: Journal of Nutrition and Athletic Excellence, which contains articles on IF. (Click here to take a look)