Stephen Phinney’s opinions on the diverse variations of the low carb diet

Lots of writers in the fitness world recommend « carb cycling » – eating carbs only after workout so you can replenish your glycogen stores.  Obviously this will end the Nutritional Ketosis.

Most writers in the fitness world who promote eating variations of low carb are usually eating too much protein and/or carbs to ever get into the keto-adapted state.  Since they have not achieved the benefits of ketones as an alternative to glucose, they quite logically might be compelled to return to carbs to maintain minimal fuel flow to the brain.

What do you think of “slow-carb” promoted by Tim Ferriss? And of the concept of “cheat-days” which are very popular in many diets? Does it makes sense to you?

These make sense only if you are not in ketosis, and you don’t need the natural anti-oxidant defenses that BOHB provides.  Has Tim Ferriss published any scientific research supporting his opinions?  I understand that he is a brilliant marketer, but so are the folks who brought us Coca Cola.

Any comment on vegan/ vegetarian diets?

There is a chapter on how to do a vegetarian low carb diet in “The New Atkins for a New You’ (co-authored by Westman/Phinney/Volek).

What do you think of intermittent fasting (becoming very popular those days)? Do you actually think that the number of meals matter for the human metabolism? Could this help you get in ketosis mode faster?

You might get into ketosis faster, but at the expense of muscle protein loss.  On the first day of a total fast, a typical person who is not keto-adapted looses 16 grams of nitrogen, which represents about half a kg of wet weight muscle coming out in the urine.  Under optimum dietary conditions, the fastest an adult can gain nitrogen by building muscle is 4 grams per day.  So for every fasting day, you would need at least 4 optimium feeding days to recover back to baseline.

What do you think of the use of supplements? I just read in “the first 20 minutes” that when you load your body with anti-oxydants it actually impairs the body’s capability do deal on it’s own with free radicals, which is consistent with the Science paper, actually.  And when I tried some of the famous low-carb sites “all you need in 6 pills per day” my urine was shining in the dark – so I’m not sure that there was much left in my body!

As I have noted, the blood level of BOHB easily achieved on a ketogenic diet has been recently shown to markedly up-regulate the body’s own natural defenses against reactive oxygen species (aka free radicals).  There is no drug or supplement available that is anywhere near this potent.  BOHB is strongly protective against damage to protein (protein carboxylation) and membrane polyunsaturated fatty acid damage (lipid peroxides),

A couple more questions from a wanabee biochemist !

How much effort do you think it takes for a normal human body to exhaust all it’s glycogen reserves?

If your question is “how long must one exercise to ‘hit the wall’ or ‘bonk’ »?  The answer depends upon how much glycogen you started with, how much carbs you consume during the effort, and how rapidly your body uses the glycogen it has in the liver and muscles.  In the keto-adapted state, a person starts with less (eg, 50% of normal in my bike racers), but they used it a one quarter the rate they did before the ketogenic diet.   And as I pointed out above, burning stored triglyceride releases not just fatty acids, but also glycerol that the body can use to make new glucose.

In functional terms, I have worked with a number of ultra-athletes, many of them physicians and scientists with a passion for self-experimentation.  One ran more than 20 marathons on a high carb diet, and was always flirting with hitting the wall before he hit the finish line (no matter how many gels and glucose drinks he could choke down).  His longest ever run was 50 km, which ended in the worst bonk of his life.  Then he switched to low carb and 3 months later ran a zero carb marathon with no bonk.  Six months after that he ran a 100 km event on a very hot day (more than half of the entrants did not finish).  He ate maybe 400 in-race kcal, maintained adequate hydration, and ran the last 15 km with a big smile because he knew he was ‘bonk-proof!’

Another MD in British Columbia has done the Victoria half-Ironman for 25 years.  Now over age 60 and struggling with his weight, he switched to a WFLCD.  On increasing zero-carb training runs, he tried without success to induce a bonk.  So last month, he had his last meal on Friday afternoon, drove to the race start Saturday morning and had 2 cups of black coffee.  Then he did this year’s half-ironman on zero carbs, trotted past the only guy in his age class ahead of him during the run, and finished first in his class and within 20 minutes of his PR for the course.  No bonk!

So if ‘running out of glycogen reserves’ means you bonk, somehow that does not happen in the keto-adapted state.

Does ketosis changes the way the mitochondria work? Or does it “force” the body to generate more mitochondria in the muscle cells which will be better at using fat as fuel (my very limited understanding is that in the Krebs cycle both can be used as fuel so I’m not sure how the adaptation happens – hence the question)

We would love to know this, but this takes muscle biopsies and very careful histology to determine.  That costs money, and we in this field remain the scientific equivalent of ‘starving artists’ …

I read recently that insulin is actually an anabolic – and therefore that eating carbs and protein at night would help build muscle. Wouldn’t being in ketosis mode make it more difficult to build muscle (specially when you get old) ?

Yes, this claim is still found in popular articles and in textbooks.  But it is again a narrowly-defined reductionist claim.  The other potent anabolic stimulus for muscle protein synthesis is the blood level of the branched chain amino acids (BCAA) – leucine, isoleucine, and valine.  There are any numbers of supplements that claim to contain extra BCAA to boost muscle growth.  Again going back to my 1983 study in bike racers, we demonstrated that the BCAA levels were increased by 25-40% on the ketogenic diet despite eating the same amount of protein.  Thus, even though their insulin levels were reduced, the increase in blood BCAA levels would more than compensate for the loss of insulin.  Isn’t nature interesting…

So you are saying that a nutritional ketosis also increases the level of BCAA? How is this possible?

Well without getting in too much detail about biochemistry, here is the basic idea : a BCAA molecule is very similar to a short-chain fatty acid, the main difference being that there are some nitrogen atoms in the chain – the fatty acid being only carbon, oxygen and hydrogen. The BCAA can be “deaminated”, which means that the nitrogen is removed and it can be used as fuel by the mitochondria, because a deaminated BCAA has the same chemical structure as an short chain fatty acid.  But if the body is used to burn ketones or fatty acids as fuel, then less BCAA are deaminated to be used as fuel, and more is available to build muscle.

Now let’s talk about running !

I’m a marathon runner and I always train on the morning with an empty stomach and 2 cups of coffee. My training can range from 45 minutes of light jogging to 2 ½ hours of quite intense running, including high speed intervals. Does it means I’m keto-adapted? Of just able to burn fat easily?

What did you eat for the month before your 2.5 hrs run?  If you were on low carb, then you are keto-adapted.  If you ate a high carb diet until the night before, you can’t keto-adapt in a few hours of running.

I chicken out when I run a marathon and I use gels along the race. Am I getting the best of both worlds or would it be better to actually run in a ketosis state?

People have to figure this out for themselves, because we are all different.  In the Western States Run, the low carb runners tend to take one 100 kcal gel per hour.  This translates into about 1500 ‘in-race kcal’ to complete the event.  But that’s against a total expenditure of 12000 -14,000 kcal to get to the finish line.  For high carb runners, they have learned that they need to ingest a minimum of 6000 kcal of carbs or they won’t finish.  Thus the low carb runners are able to use 4-5000 more kcal of body fat during the race compared to those on high carb.

Are those 100 kcal per hour really necessary?  As noted above, I know of a few daring souls who have completed 100 mile runs or half-Ironman events on zero or near-zero carbs.

Usually even after a significant effort (more than 1 hour of running) my glycemia is higher than when I wake up (like 100 or 110). I guess that it’s the glycogen that is still flowing in my body to fuel my effort.  Still it seems odd!

Increased blood glucose during exercise is a well-known effect.  Glucose levels only fall just before a bonk.  In our study of bike racers, there was less up and down fluctuation of glucose during exercise after adaptation to the low carb diet.

Tim Noakes, in his book “waterlogged” explains that there is some type of placebo effect in the brain : if your tongue senses carbs, even if you don’t swallow them, you can produce a more intense effort.  So even if he is a strong advocate of low carb he recommends some type of carbs during competition.

This remains to be objectively explored.

A bit of culture as a conclusion …

Why do you think it’s so difficult for people to change their diet and /or realize that they are killing themselves by having the wrong diet/lifestyle? I have noticed, since I went into low-carb diet, and trying to promote it, that I get the same type of emotional reaction talking about diet than about … religion, or politics. 

Getting enough food has always been a necessity for life, and we can speculate that most of our ancestor’s life – and culture – revolved around food: accumulating knowledge about food locations, recipes, plants to eat and not to eat, was just vital for the groups survival. In that respect developing norms and sticking to them is probably deeply engrained in our brains, and is part of our innate make-up, like language or basic physics. We could speculate that one of the initial functions of culture was to save what was vital for the group survival and ensure group’s behavior conformity, as alternative behavior may jeopardize the group’s survival. Which is probably why the tribe harvesting the fat from the “Hoolichan fish” treated it as a god send. So compliance to group behavior, which is something that is already a common feature of humans, is probably even stronger when it comes to food – and a reason why it’s very difficult for humans to eat differently from their reference group. Not to mention the addictive properties of sugar, and the fact that we were engineered by nature to live in a world where food would be scarce and require significant energy to grab – much more than opening you fridge or driving to the supermarket!

Besides your books, which resources would you recommend for people interested in Nutritional Ketosis?

Nutritional Ketosis remains a rather toxic topic, so only brave souls and fools tend to populate this space.

Thanks Stephen for your time and for promoting a healthier world!  

Now who’s willing to try Nutritional Ketosis ? 

I definitely am !