Manipulating Evidence

RunnersWeb.com yesterday had an article written by Kimberly Mueller-Brown, MS, RD - Science of Sport: Are the Atkins, Zone, and South Beach Diets Slowing you Down?

Ms. Mueller-Brown is obviously convinced that a high-carbohydrate diet is best and is intent on showing why. Not only that, she puts forth an extensive listing of "evidence" to support her position and convince her readers! Unfortunately in her zeal to prove a high carbohydrate diet is best, she ignored much of the data available that undermines her position. Not that I’m surprised, after all, she is trying to make the case that if you’re an athlete you’ll do poorly with a low-carb diet!

She states, "Here are the top ten reasons why high carbohydrate diets win the race."

Before we take a look at her "evidence," let me state the obvious - low-carb diets are most appropriate for weight loss or to manage specific metabolic disorders…and most runners aren't inclined to be severely overweight or obese and I’d hazard a guess that few are suffering with the major metabolic dysfunctions that low-carb diets tend to reverse.

That said, there is ample evidence that shows that one can participate in endurance sports, including running, while consuming a low carbohydrate diet and I see absolutely no reason why an endurance athlete won't do well with controlled-carbohydrate dietary approaches.

So then, where does Ms. Mueller-Brown start?

She starts by laying the foundation that it is well established that high carbohydrate diets are better for athletes and puts forth the current position statements of various health organizations. Nothing new here and no evidence presented to support the idea that low-carb negatively affects performance – she simply states the position of those who are adamant that low-fat, high carbohydrate diets are optimal for everyone.She then moves forward to list the top ten reasons why low-carb diets are bad.

#10: Low carbohydrate diets leave you mentally drained

If you are following a low carbohydrate regimen, it is no wonder since the minimal amount of carbohydrate grams suggested for optimal mental functioning is listed at 130 grams or just over 500 calories. During the induction phase, Atkins followers are encouraged to keep carbohydrate intake to no more than 20 grams per day; if you are running enough, you can boost that up to 60-90 grams per day. You can see where this may be a problem. Approximately 75-100 grams (300-400 calories) of carbohydrate can be stored within the liver as glycogen. The energy stored within the liver helps maintain blood sugars and also fuels both the brain and working muscles. With blood sugars naturally rising and falling in 2-4 hour increments depending on metabolic efficiency, liver glycogen stores constantly need to be replenished with snacks consisting of some carbohydrate. When inadequate carbohydrates are consumed, liver glycogen levels fall quicker, causing blood sugars to drop; a lack of fuel being sent to the brain triggers dizziness, fatigue, headaches, and an overall feeling of sluggishness known as “bonking.”

Evidence presented to support her contention? None.

She does put forth a "logical" rationalization for her position, but no supporting evidence is provided. So, at best this is speculation.

The question is, has anyone studied the effect of low-carb diets and mental cognition?

Suicide is probably an action most indicative of mental instability. Researchers in 2005 found that it was low intake of polyunsaturated fats that distinguished those who attempted suicide from those who didn’t. Now while this particular study did not compare low-carb and high-carb diets, it is an important piece of the puzzle regarding mental health – and this particular study implicates a deficiency in fat, not carbohydrate, in the diet.

Back in 1985, in an absolute zero carbohydrate trial, researchers found that “There was no support for the idea that a minimal-carbohydrate, protein-supplemented fast decreases appetite and elevates mood more in comparison with a similar diet containing enough carbohydrate to minimize ketosis.” This was due to the results showing that BOTH groups of dieters investigated reported similar feelings on their respective diets.

In 2002, researchers concluded that “The results show that both absolute cortisol levels and net cortisol increase were greater in the glucose group in comparison to the other groups "

Her real error with this one is her lack of understanding human metabolism. She insists that “glycogen stores constantly need to be replenished with snacks consisting of some carbohydrate." To this I have just one word: gluconeogenesis.

#9 Low carbohydrate diets trigger premature muscle fatigue during exercise

Athletes following lower carbohydrate regimens, however, have been shown to store approximately 45-75% less glycogen as compared to their “carbo-loading” training buddies. Therefore, athletes are more vulnerable to premature depletion of muscle glycogen, ultimately compromising muscle function and leading to debilitating cramps, slowed pace, reduced power output, and diminished endurance capacity, otherwise known as “hitting the wall.”

Evidence presented?

9. Sherman, W.M, Costill, D.L., Fink, W.J., and J.M Miller. Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. Int. J. Sport Med. 2:114-118, 1981.
10. Kavouras, S.A., Troup, J.P., and J.R. Berning. The influence of low versus high carbohydrate diet on a 45-min strenuous cycling exercise. Int. J. Sport. Nutr. Exerc. Metab. 14: 62-72, 2004.
11. Widrick, J.J., Costill, D.L., Fink, W.J., Hickey, M.S., McConell, G.K., and H. Tanaka. Carbohydrate feedings and exercise performance: effect of initial muscle glycogen concentration. J. Appl. Physiol. 74: 2998-3005, 1993.
12. Williams, C., Brewer, J., and M. Walker. The effect of a high carbohydrate diet on running performance during a 30-km treadmill time trial. Eur. J. Appl. Physiol. 65: 18-24, 1992.

Numbers 9, 11 and 12 are exclusively looking at high carbohydrate and therefore offer no insight into differences between high carbohydrate versus low carbohydrate diets on performance.

Number 10 is interesting and does indeed look at the influence of a high-carb versus low-carb diet on endurance. Why she included it as an indictment against low-carb diets is beyond me - here is what the researchers concluded: No significant changes were observed in serum free fatty acid, triglycerides, or insulin concentration in either trial. The findings suggest that L-CHO had no major effect on 45-min cycling exercise that was not observed with H-CHO when the total energy intake was adequate.

No major effect? Gee, who knew...

Now a very interesting look at elite athletes was conducting in 2004, specifically reviewing the diet of elite athletes in Greece. Guess what the researchers found? Mean carbohydrate consumption for male and female athletes was 4.5 g/kg and 3.8 g/kg of body weight, respectively. Fat intake was 153 g for males and 79 g for females… The data suggest that athletes of both genders consumed too much fat and too little carbohydrate. Elite athletes consuming less carbohydrate? Just how do they perform?

How about in 2003 researchers investigated high carbohydrate versus low carbohydrate diets on fatigue and concluded that “As the reductions in muscle glycogen, CP, and SR function during exercise were not different by dietary treatment, these data do not support a link between whole muscle glycogen and SR function or CP reduction during repeated sprint exercise.”

Now in 2000, researchers addressed the question of high carbohydrate intake and performance and found that those with high fat intake actually had better endurance! “Based on this review, a baseline diet comprising 20% protein, 30% CHO and 30% fat, with the remaining 20% of the calories distributed between CHO and fat based on the intensity and duration of the sport, is recommended for discussion and future research.”

Dr. Stephen Phinney found that "Impaired physical performance is a common but not obligate result of a low carbohydrate diet. Lessons from traditional Inuit culture indicate that time for adaptation, optimized sodium and potassium nutriture, and constraint of protein to 15-25 % of daily energy expenditure allow unimpaired endurance performance despite nutritional ketosis." in his study, "Ketogenic diets and physical performance"

In another study, The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation, he found that "the results indicate that aerobic endurance exercise by well-trained cyclists was not compromised by four weeks of ketosis. This was accomplished by a dramatic physiologic adaptation that conserved limited carbohydrate stores (both glucose and muscle glycogen) and made fat the predominant muscle substrate at this submaximal power level."

#8 Low carbohydrate diets compromise immune function

The immune suppression seen in runners may also be attributed to elevated levels of the stress hormone cortisol and a corresponding drop in lymphocyte production and T-cell activity seen after completion of hard training. Interestingly, low carbohydrate diets, specifically those yielding carbohydrate intakes less than 30 grams, seem to exacerbate this effect.

Well, here's a new one. So, what's the evidence?

13. Parry-Billings, M., Budgett, R., Koutedakis, Y., Blomstrand, E., Brooks, S., Williams, C., Calder, P.C., Piling, S., Baigrie, R., and E.A. Newsholme. Plasma amion acid concentrations in the overtraining syndrome: Possible effects on the immune system. Med. Sci. Sports Exerc. 24: 1353-1358, 1992.
14. Gleeson, M., Blannin, A.K., Walsh, N.P., Bishop, N.C., and A.M. Clark. Effect of low- and high-carbohydrate diets on the plasma glutamine and circulating leukocyte response to exercise. Int J. Sport Nutr. 8: 49-59, 1998.
15. Nieman, D.C. Nutrition, exercise, and immune system function. Clinics in Sports Med. 18: 537-548, 1999.

Again, we have data that isn't apples-to-apples specifically looking at low-carb versus high-carb except in one reference.

So, what does that reference - #14 - tell us? Not much - the researchers investigated the effect of a high-carb versus low-carb diet after just three days of eating one or the other to reach their conclusions. Now this isn't necessary a bad thing, it's just that a good amount of data exist that show an individual needs at least 2-weeks to adapt to the low-carb diet before performance rebounds to pre-low-carb levels.

Again, I'll cite Stephen Phinney. Dr. Stephen Phinney found that "Impaired physical performance is a common but not obligate result of a low carbohydrate diet. Lessons from traditional Inuit culture indicate that time for adaptation, optimized sodium and potassium nutriture, and constraint of protein to 15-25 % of daily energy expenditure allow unimpaired endurance performance despite nutritional ketosis." in his study, "Ketogenic diets and physical performance"

In another study, The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation, he found that "the results indicate that aerobic endurance exercise by well-trained cyclists was not compromised by four weeks of ketosis. This was accomplished by a dramatic physiologic adaptation that conserved limited carbohydrate stores (both glucose and muscle glycogen) and made fat the predominant muscle substrate at this submaximal power level."

But then again, his research didn't look at nutrients. Has anyone looked at nutrients or their factors? Yes...

In 2002 researchers investigated the antioxidant levels in women following high carbohydrate versus low carbohydrate diets. They concluded that “It seems justified to presume that higher daily doses of haem iron, selenium and alpha-tocopherol provided by the L-CHO diet contributed to the enhancement of catalase activity, the rise in plasma concentrations of alpha-tocopherol and selenium, which resulted in better protection of the cell membranes against damage from peroxides, as reflected by a limited release of creatine kinase into plasma. With the exception of the case of glutathione reductase, the phases of the menstrual cycle had only minor effects on the indices of the blood antioxidant defence system.”

#7 Low carbohydrate diets affect mood

Judith Wurtman, director of the Women’s Health Program at the Massachusetts Institute of Technology and the Adara Weight Loss Center, has conducted studies on rats showing a connection between low carbohydrate intake and low levels of serotonin – a neurotransmitter that promotes feelings of happiness and satisfaction. In her research, rats placed on a ketotic, or low-carbohydrate diet for three weeks were found to have lower levels of serotonin in their brains. Wurtman believes that same effect occurs in humans on low-carb diets, leading to pronounced feelings of depression and sadness, even rage.

I've heard this one repeated a number of times, and expected to see it here too.

So, what's the evidence?

16. Wurtman, R.J., and J.J. Wurtman. Carbohydrates and depression. Sci Am. 260(1): 68-75, 1989.

Nothing new since 1989? Wow.

Wait a minute, there has to be more research available from the last, oh, 17 years!

First let’s start with some of Dr. Wurtman’s findings since 1989, in 1995 her research showed that “This ability of neurons to couple neuronal signaling properties to food consumption is a link in the feedback mechanism that normally keeps carbohydrate and protein intakes more or less constant. However, serotonin release is also involved in such functions as sleep onset, pain sensitivity, blood pressure regulation, and control of the mood. Hence many patients learn to overeat carbohydrates (particularly snack foods, like potato chips or pastries, which are rich in carbohydrates and fats) to make themselves feel better. This tendency to use certain foods as though they were drugs is a frequent cause of weight gain, and can also be seen in patients who become fat when exposed to stress, or in women with premenstrual syndrome, or in patients with "winter depression," or in people who are attempting to give up smoking. (Nicotine, like dietary carbohydrates, increases brain serotonin secretion; nicotine withdrawal has the opposite effect.)”

In 1994, she also had research published that implicated carbohydrate in obsessive-compulsive disorder, “This finding of different snacking patterns in OCD mirrors that found in other disorders that have been shown to be responsive to serotonergic drugs. The high incidence of carbohydrate snacking among OCD patients compared with the control group provides additional evidence that brain serotonin may be involved in this disorder.”

A study this year, Malabsorption of carbohydrates and depression in children and adolescents, showed some interesting results - 71.42% of those found to be "sugar intolerant" displayed symptoms of depression, compared with just 15% of the control group.

In a study in 2002, researchers found that only individuals with high stress sensors (compared with individuals classified as having low stress sensors) were sensitive to carbohydrate in the diet. It was only the high stress sensor individuals who had a measurable difference in mood after a carbohydrate rich meal.

In a 1999 review, researchers found vitamin deficiencies were more to blame than macronutrient mix for depression in a wide range of depressed individuals.

Can diet affect mood? Sure. But it's not high carbohydrate that's the cure!

#6 Low carbohydrate diets are often deficient in essential nutrients

With a lack of grains, fruits, and vegetables being consumed in low carbohydrate diets, runners run the risk of developing dietary deficiencies of key nutrients including dietary fiber, which can affect digestive health; vitamin C, which can compromise immune function; folic acid, which may elevate risk for cardiovascular disease; and magnesium, which may elevate risk for cramping and also compromise bone health. A lack of fiber also increases your risk for cancers of the digestive track (because transit time is lengthened) and cardiovascular disease (because of fibers effect on fat and cholesterol). Low carbohydrate diets lack in the phytonutrients / antioxidants found in fruits, vegetables, legumes, and whole grains, all proven to aid in prevention of cancer and heart disease.

I think in the last six months I’ve provided ample evidence, by way of actual menu samples posted, that if you follow a low-carb diet correctly, you meet or exceed nutrient requirements. The opposite is true of the low-fat diets out there.

But, what evidence does Ms. Mueller-Brown provide?

17. Bravata, D.M., Sanders, L., and J. Huang et al. Efficacy and safety of low-carbohydrate diets: a systematic review. JAMA. 289:1837-50 [review], 2003.
18. Brehm, B.J, Seeley, R.J., Daniels, S.R., and D.A. D'Alessio. A randomized trial comparing a very low carbohydrate diet and a calorie-restricted low fat diet on body weight and cardiovascular risk factors in healthy women. J Clin Endocrinol Metab. 88:1617-23, 2003.

Well, let’s see…#17 didn’t look at micronutrient content of low-carb diets at all. Interestingly, the researchers conclusion was, “There is insufficient evidence to make recommendations for or against the use of low-carbohydrate diets, particularly among participants older than age 50 years, for use longer than 90 days, or for diets of 20 g/d or less of carbohydrates.”

Number 18 also did not evaluate low-carb diets for micronutrient content. Again, researchers concluded that “Based on these data, a very low carbohydrate diet is more effective than a low fat diet for short-term weight loss and, over 6 months, is not associated with deleterious effects on important cardiovascular risk factors in healthy women.”

Not exactly the type of indictment you’d expect for this category, eh?

As I've already cited, in 2002 researchers investigated the antioxidant levels in women following high carbohydrate versus low carbohydrate diets. They concluded that “It seems justified to presume that higher daily doses of haem iron, selenium and alpha-tocopherol provided by the L-CHO diet contributed to the enhancement of catalase activity, the rise in plasma concentrations of alpha-tocopherol and selenium, which resulted in better protection of the cell membranes against damage from peroxides, as reflected by a limited release of creatine kinase into plasma. With the exception of the case of glutathione reductase, the phases of the menstrual cycle had only minor effects on the indices of the blood antioxidant defence system.”

#5 Low carbohydrate diets slow muscle recovery

Consumption of carbohydrate-rich foods post-exercise will help enhance recovery from workouts. Carbohydrate-rich foods cause a more rapid rise in blood glucose, which in turn triggers the release of insulin or the “master recovery hormone.” Insulin, the same hormone knocked by Dr. Atkins (Atkins Diet), Dr. Barry Sears (Zone Diet), and Dr. Agatston (South Beach Diet), actually facilitates the transport of carbohydrate, specifically glucose, from the blood into the muscle cell where it can be metabolized to produce energy that will prepare the muscle cell to do work again. Within 30-60 minutes post-exercise, consumption of a carbohydrate-rich snack plus a small amount of protein (e.g., banana mixed in low-fat yogurt) has been shown to triple the rate of muscle glycogen replenishment and muscle protein synthesis. Furthermore, as compared to a protein-only supplement taken post exercise, a carbohydrate-protein solution has been shown to enhance rate of glycogen storage by 5 times, thereby facilitating muscle recovery.

Now this one is interesting. It isn’t one of the major complaints you hear everyday. How about we look at the evidence presented to support this contention.

19. Levenhagen D. L. et al. Post-exercise nutrient intake timing in humans is critical to recovery of leg glucose and protein homeostasis. Am J Phys, Endocrin Met. 280: E982-E993, 2001.
20. Zawadzki K.M., B.B. Yaspelkis, J.L. Ivy. Carbohydrate-protein complex increases the rate of muscle glycogen storage after exercise. J Appl Phys. 72, 1854-9, 1992.

Her first study didn’t look at low-carb or compare differences in macronutrient mix in the recovery process, so this one is moot.

Her second study was an interesting look at ingesting carbohydrate or protein alone after a workout or a combination of carbohydrate and protein. But, it didn’t look at an athlete following a low-carb diet that had adapted to the low-carb diet. Sorry, but this apples to oranges try is not worthy of comment. A review of the literature shows that no one has actually taken the time to study muslce recovery time while following a low-carb diet. So, at best, the jury is still out.

#4 Low carbohydrate diets increase risk for muscle injury during training

With a low carbohydrate intake during endurance training, this is inevitable since there is increased protein breakdown and consequent loss of lean body weight. Furthermore, the biomechanics of your running stride may be negatively affected due to cramping and muscle fatigue (also associated with depletion of muscle glycogen stores), aka “the wall”, thereby causing a variety of new aches and pains as well as muscle tightness. Finally, when insulin levels are chronically low, as they often are with a very low carbohydrate intake, catabolism (breakdown) of muscle protein increases, and protein synthesis is hindered.

21. Kimball, S.R, Vary, T.C, and L.S. Jefferson. Regulation of Protein Synthesis by Insulin. An. Rev. Phys. 56:321, 1994.

Interestingly this one is no longer available online – and why should it be, it’s an annual review from 1994! Surely we have more data now, some 12 years later – wouldn’t you think?

Like number 5, no studies are found in the literature to really say one way or the other. So, at best, jury is still out on this one too.

#3 Low carbohydrate diets increase risk for kidney stones

#2 Low carbohydrate diets can diminish bone health

When following a high protein, low carbohydrate meal plan, both uric acid and calcium oxalate stones are more likely to form. In fact, one study found that consumption of a low carbohydrate, high protein diet for 6 weeks delivers a marked acid load to the kidney, increasing the risk for stone formation.

Individuals consuming a higher ratio of protein to carbohydrates run the risk of developing brittle bones or osteoporosis. When the body digests protein, the kidneys work overtime to filter the toxic byproducts produced during breakdown of protein. Once filtered, protein is excreted in the urine; however, along with protein, there is increased urinary loss of calcium, which can ultimately compromise your bone health, thereby increasing your risk for bone fracture. In fact, consumption of a low carbohydrate, high protein diet over 6 weeks has been shown to significantly decrease estimated calcium balance and may increase the risk for bone loss and stress fracture. Injury of the bone will definitely inhibit maximum fitness performance.

This one is so old, yet repeated time and again even though there is no real data to support the contention. But, let’s at least give her credit for trying! What eveidence does she provide?

22. Reddy, S.T, Wang, C.Y., Sakhaee, K., Brinkley, L., and CYC. Pak. Effect of low-carbohydrate high-protein diets on acid-base balance, stone-forming propensity, and calcium metabolism. Am. J. Kidney Dis. 40(2):265-74, 2002.

Nice try! In this one the researchers indeed made a negative conclusion about low-carb diets, “Consumption of an LCHP diet for 6 weeks delivers a marked acid load to the kidney, increases the risk for stone formation, decreases estimated calcium balance, and may increase the risk for bone loss.” Key word in the conclusion, "may."

However, studies that were published AFTER this one shot this idea down quickly.

April 2005 a study was published that found “The magnitude of weight loss and the improvements in insulin resistance and cardiovascular disease risk factors did not differ significantly between the 2 diets, and neither diet had any detrimental effects on bone turnover or renal function.”

Another study from 2005 found that high protein versus lower protein was “each diet had either no or minimal effects on lipid levels (total cholesterol, low-density lipoprotein, high-density lipoprotein), renal (blood urea nitrogen, serum creatinine), or hepatic function (aspartate aminotransferase, alanine aminotransferase, bilirubin).”

2003 brought a study that showed “Bone density did not change. Conclusions - A low energy diet high in red meat seems to provide a weight loss advantage to subjects with some features of the metabolic syndrome with no adverse effects on bone metabolism.”

#1 Low carbohydrate diets can trigger joint pain

Protein-rich sources such as meats, poultry, seafood, and eggs commonly consumed as part of a high protein regimen contain high levels of purines, which raise blood levels of a compound called uric acid. An excess of uric acid in the body causes gout, which is a form of arthritis. Elevated levels of uric acid in the blood may lead to needle-like uric acid crystals in joints, triggering pain. A new study published in the New England Journal of Medicine has confirmed the correlation between high protein intakes and gout. The researchers studied 47,150 men who had no history of gout at the beginning of the study. During the 12 years of the study, they documented 730 confirmed cases of gout. The relative risk of gout among men was highest among men with the highest intake of meat and seafood. They concluded that higher levels of meat and seafood consumption, like that seen in low carbohydrate meal plans, are associated with an increased risk of gout.

23. Choi, H.K, Atkinson, K., Karlson, E.W., Willet, W., and G. Cuhan G. (2004). Purine-rich foods, dairy and protein intake and the risk of gout in men. N. Engl. J. Med. 350: 1093-1103, 2004.

Did this study look at low-carb diets? No. It was looking at the effect of purine-rich foods in a typical diet and the incidence of gout.

A study last year that looked at carbohydrate intake and gout concluded that “The results suggest that weight reduction associated with a change in proportional macronutrient intake, as recently recommended in IR, is beneficial, reducing the SU levels and dyslipidaemia in gout. Current dietary recommendations for gout may need re-evaluation.”

In 2001 the use of low carbohydrate diets for gout specifically was started and we find this in a review from that year that states, “A low carbohydrate, high protein and unsaturated fat diet was recommended for gouty patients since they all enhance insulin sensitivity and therefore may promote a reduction in serum uric acid levels.”

My take away message - just because someone lists a bunch of research in their bibliography doesn't mean it's applicable to their arguement. I've shown that much of her "evidence" did not look at low-carb diets and those that did actually reached different conclusions than she said they did! I've provided links to every last research study I've countered with - please take the time to read those that interest you so you can gain knowledge about this area of dietary research!