Monday, February 18, 2008

Low-Carb diets & Entropy

Back in October of last year, Dr. Michael R. Eades wrote an interesting post about one way in which low-carb diets work by providing a metabolic advantage over any isocaloric diet of different macronutrient proporitions (ie. a high carb diet). Proponents of the "A Calorie is a Calorie" concept argue that suggesting such an advantage exists defies the laws of thermodynamics and therefore can not be true. The law that they are talking about is the 1st Law of Thermodynamics, or the Law of Conservation of Energy, which states:

"The increase in the internal energy of a system is equal to the amount of energy added by heating the system, minus the amount lost as a result of the work done by the system on its surroundings."

Simply stated, and in reference to the body and nutrition, energy can neither be created or destroyed, so Calories in (food) must = Calories out (metabolism, exercise, etc.). Unfortunately, the universe isn't that simple. Eades uses the 2nd Law of Thermodynamics to show this. This law, which states:

"The entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium."

What this means is that you can't turn 100kcal of pasta into 100kcal of activity, some of that 100kcal is lost as heat, which depends on what type of calorie it was (carb, protein, fat). This changes the Calories in = Calories out equation to Calories in = Calories out + Entropy (the energy lost to the universe, usually as heat, during any chemical reaction).

How all of this applies to weight loss and low-carb diets is that the entropy created in converting non-carbohydrate macronutrients (fat, protein) into blood sugar for energy is much greater than that created by carbohydrates into blood sugar (carbs = sugar). Fat and Protein doesn't convert to blood sugar easily. It takes many steps and many different chemical reactions, all of which result in a loss of heat to the universe. All of these extra steps means that your body has to expend more energy, and the lost heat results in a higher basal metabolic rate, which means that you burn more calories at rest. This result has been shown in the following study which Eades provided reference to.

The bottom line: if you take two people, put them on isocaloric diets, one that is low-carb, and one that is high-carb, the person on the low-carb diet should lose more weight because they are having to expend more energy to convert fat and protein to sugar.

Monday, October 22, 2007

Gary Taubes on Larry King Live

Gary Taubes appeared on Larry King Live last Friday to talk about his new book, Good Calories, Bad Calories. Unfortunately, the zealots that they brought on the show to debate with him don't ever give him a chance to speak, so the message falls flat and on deaf ears. It's at least worth checking out, here's the link.

Thursday, September 20, 2007

Correlation Does Not Equal Causation

Gary Taubes, author of "The Soft Science of Dietary Fat", "What if it's all been a big fat lie?", and the forthcoming book "Good Calories, Bad Calories", recently wrote an excellent article for the New York Times entitled "Do We Really Know What Makes Us Healthy?". The article discusses the successes and failures of epidemiological studies, the kind that produce results like "Saturated fat increases the risk of heart disease" or "H.R.T. in post-menopausal women decreases the risk of osteoporosis". They are broken down into two types of studies. The first, which are strictly observational, are the kinds that you hear about the most in the media, and which provide the foundation for the majority of public health "knowledge". The second, which are ideally double-blind, randomized clinical trials, try to control as many variables as they can to either prove or disprove an observation or set of observations obtained from the first study. The issue, as Taubes elegantly explains, is that neither can determine causation, and the types that would provide meaningful results are so costly, time consuming, and likely un-ethical, that it is unrealistic to expect that they will ever be performed. It's a great read, and really puts the issue of public health information into perspective. His book comes out at the end of this month; I am anxiously awaiting its release.

Tuesday, July 31, 2007

Oxidative Stress, Aging, and Endurance Training

I always wondered why endurance athletes looked older than they should, I had a theory developed, and now I found someone who seems to agree with that theory. Mark Sisson, a former endurance athlete himself, wrote a great piece in his blog about pre-mature aging amongst endurnace athletes. Here are the cliffnotes:

- Carbohydrate metabolism is costly and inefficient. Your muscles and liver can only hold 500-600g of glycogen, which will only fuel about 2 hours of endurance activity at best. Therefore endurance athletes need to consume lots of carbs.

- Lots of carbs means lots of insulin, which means lots of inflammation.

- Chronic glycogen depletion means chronically high levels of Cortisol, which suppresses immune function, reduces calcium uptake, and reduces lean mass in addition to many other negative side effects.

- Beta-Oxidation of fats during training generates free-radical damage at a rate of up to 20 times what is possible at rest.

If you need further explanation of why all of these effects are bad, and how they add up to pre-mature aging, cancer, heart disease, and massive lean tissue degradation, read the entire article.

Friday, July 27, 2007

Unhappy Meals

Michael Pollan, author of The Omnivore's Dillema, wrote a great common sense article for the New York Times back in January (I know, it was 6 months ago, but if you haven't already noticed, I don't keep up with the times very well). The article, titled Unhappy Meals, has a simple message:

Eat food. Not too much. Mostly plants.

While I don't agree with his meat-as-a-side-dish views, the key to his message is the Eat food portion. What is meant by this is simple:

"’re much better off eating whole fresh foods than processed food products. That’s what I mean by the recommendation to eat “food.” Once, food was all you could eat, but today there are lots of other edible foodlike substances in the supermarket. These novel products of food science often come in packages festooned with health claims, which brings me to a related rule of thumb: if you’re concerned about your health, you should probably avoid food products that make health claims. Why? Because a health claim on a food product is a good indication that it’s not really food, and food is what you want to eat."

It seems pretty common sense, but I'm constantly amazed when clients bring me food products that they think are healthy because they have some health claim printed on their package. This is why I love the Paleo Diet so much, it's simple. If you stick to eating meat, fruits, vegetables, and nuts, you don't have to worry about what effects all of the un-pronounceable ingredients on the package of your food are going to have on your body, because real food doesn't come in a package with a list of ingredients.

Thursday, June 7, 2007

Paleo Today

I found this great article on The Paleo Diet website that provides an example of what the paleo diet would look like using modern foods, complete with a nutritional profile of the diet detailing macro and micronutrient content. What was found is that it is entirely possible to consume a nutritionally balanced diet using modern foods that mimic the food groups and types that were available to paleolithic man. The relative contribution of various foods (plant and animal) to the diet was based on average values previously determined in numerous hunter gatherer societies. This data was used in combination with the 20 most common fruit, vegetables, and fish sold in the United States to determine the composition of the diet, detailed to the point of creating a mock 1 day menu. The diet was then analyzed for macro and micronutrient content. What is most interesting to note is the the macronutrient content of this diet turned out to be 38% Protein, 39% Fat, and 23% Carbohydrate, which closely mimics Zone proportions with a few carbs replaced with fat. The only visible shortcoming of the diet was lack of Vitamin D, which Paleolithic man would have obtained from the sun.

Thursday, April 19, 2007

Ketogenic Diets & Physical Performance

I've been experimenting with low carb eating for several months now, and there have definitely been a few bumps in the road. Whenever I attempt an intense CrossFit workout during the first few days of low carbing, I tank. The reason seems clear: I'm not eating enough carbs. Afterall, carbs are what supply the fuel for intense exercise, so it seems foolish to try to workout without them. Fortunately, there's some hope. Thanks to Robb Wolf over at The Performance Menu, I stumbled across this jewel of a study:

Ketogenic diets and physical performance


The study is a discussion of the juxtaposition of clinical research results favoring carbohydrate against observed functional well-being in traditional cultures consuming none. It begins by giving a brief history of how carbohydrates came to dominate our diet, then cites a few studies that seem to confirm the necessity of carbs for optimal physical performance.

The hunter's counterpoint – practical observations on ketogenic diets

The author begins to provide some insight into how ketogenic diets can sustain performance by citing a couple of real world examples in which explorers were forced into ketosis during their travels without any noticeable performance detriments after a period of adaptation.

Modern ketogenic diet performance studies

This is where most of the value in the study lies. The author details a couple of studies that he has performed investigating the effects of ketogenic diets on physical performance:

1st Study:

...a study of subjects given a very low calorie ketogenic diet for 6 weeks in a metabolic research ward. The protein for this diet, along with a modicum of inherent fat, was provided by lean meat, fish, and poultry providing 1.2 grams of protein per kg of reference ("ideal") body weight daily. In addition, mindful that the natriuresis of fasting could reduce circulating blood volume and cause secondary renal potassium wasting, the subjects were prescribed 3 grams of supplemental sodium as bouillion and 25 mEq (1 g) of potassium as bicarbonate daily.

Treadmill performance testing of these subjects included determinations of peak aerobic power (VO2max) after a 2-week weight maintenance baseline diet, and again after 6 weeks of the ketogenic weight loss diet. Endurance time to exhaustion was quantitated at 75% of the baseline VO2max. This endurance test was repeated again after one week of weight loss and finally after 6 weeks of weight loss. Other than these tests, the subjects did no training exercise during their participation in this study. To compensate for the fact that the average subject had lost over10 kg, the final endurance treadmill test was performed with the subject carrying a backpack equivalent in weight to the amount lost.

The energy expenditure data (expressed as oxygen consumption) and exercise times across this 8-week inpatient study are shown in Table 1 (I was unable to link to the table, but you can link to it directly from the study via the link that I provided above). That these subjects'peak aerobic power did not decline despite 6 weeks of a carbohydrate-free, severely hypocaloric diet implies that the protein and mineral contents of the diet were adequate to preserve functional tissue. As can be noted, endurance time to exhaustion was reduced after one week of the ketogenic diet, but it was significantly increased over the baseline value by the 6-week time point. However the interpretation of this endurance test is confounded by the fact that the oxygen cost (ie, energy cost) of the treadmill exercise had significantly decreased following the weight loss, and this occurred despite the subjects being made to carry a backpack loaded to bring them back to their initial exercise test weight.

This question of improved efficiency notwithstanding, it is clear that our subjects experienced a delayed adaptation to the ketogenic diet, having reduced endurance performance after one week followed by a recovery to or above baseline in the period between one and six weeks. Given the reduced energy cost of the exercise despite the backpack, the extent of this adaptation cannot be determined from this study. To explain this improved exercise efficiency, we can speculate that humans are more efficient carrying weight in a modern backpack than under their skin as excess body fat. It is also possible that these untrained subjects became more comfortable with prolonged treadmill walking by their third test, and therefore improving their overall efficiency.

2nd Study utilized competitive bicycle racers as subjects, confined to a metabolic ward for 5 weeks. In the first week, subjects ate a weight maintenance (eucaloric) diet providing 67% of non-protein energy as carbohydrate, during which time baseline performance studies were performed. This was followed by 4 weeks of a eucaloric ketogenic diet (EKD) providing 83% of energy as fat, 15% as protein, and less than 3% as carbohydrate. The meat, fish, and poultry that provided this diets protein, also provided 1.5 g/d of potassium and was prepared to contain 2 g/d of sodium. These inherent minerals were supplemented daily with an additional 1 g of potassium as bicarbonate, 3 grams of sodium as bouillon, 600 mg of calcium, 300 mg of magnesium, and a standard multivitamin.

The bicyclist subjects of this study noted a modest decline in their energy level while on training rides during the first week of the Inuit diet, after which subjective performance was reasonably restored except for their sprint capability, which remained constrained during the period of carbohydrate restriction. On average, subjects lost 0.7 kg in the first week of the EKD, after which their weight remained stable. Total body potassium (by 40K counting) revealed a 2% reduction in the first 2 weeks (commensurate with the muscle glycogen depletion documented by biopsy), after which it remained stable in the 4th week of the EKD. These results are consistent with the observed reduction in body glycogen stores but otherwise excellent preservation of lean body mass during the EKD.

The results of physical performance testing are presented in Table 2
(I was unable to link to the table, but you can link to it directly from the study via the link that I provided above). What is remarkable about these data is the lack of change in aerobic performance parameters across the 4-week adaptation period of the EKD. The endurance exercise test on the cycle ergometer was performed at 65% of VO2max, which translates in these highly trained athletes into a rate of energy expenditure of 960 kcal/hr. At this high level of energy expenditure, it is notable that the second test was performed at a mean respiratory quotient of 0.72, indicating that virtually all of the substrate for this high energy output was coming from fat. This is consistent with measures before and after exercise of muscle glycogen and blood glucose oxidation (data not shown), which revealed marked reductions in the use of these carbohydrate-derived substrates after adaptation to the EKD.

What is most interesting about these studies, particularly the second, is that sprinting capability (CrossFit Workouts) was the only performance parameter that wasn't restored after the keto-adaptation period. This is what I have observed from my own experience and through talking with others. Also, the keto-adaptation period must be strictly low carb, as the author points out:

There are to date no studies that carefully examine the optimum length of this keto-adapataion period, but it is clearly longer than one week and likely well advanced within 3–4 weeks. The process does not appear to happen any faster in highly trained athletes than in overweight or untrained individuals. This adaptation process also appears to require consistent adherence to carbohydrate restriction, as people who intermittently consume carbohydrates while attempting a ketogenic diet report subjectively reduced exercise tolerance.

This is where I've screwed up several times in the past. I can successfully go 5 days (M-F) strictly adhering to low carb eating, but somehow manage to indulge on the weekends. It's a vicious cycle in which I never become keto-adapted, and have to constantly supplement my diet with carbs in order to maintain high levels of performance. Even after becoming keto-adapted, unless I keep my exercise intensity low by focusing on strength routines and steady-state cardio, my performance will suffer, as the author notes in his conclusion:

Therapeutic use of ketogenic diets should not require constraint of most forms of physical labor or recreational activity, with the one caveat that anaerobic (ie, weight lifting or sprint) performance is limited by the low muscle glycogen levels induced by a ketogenic diet, and this would strongly discourage its use under most conditions of competitive athletics.

The question now becomes: Can you STAY keto-adapted while adding in some post-workout carbs to replenish your glycogen stores? I'll be sure to write a post on that as soon as I figure it out.