Saturday, February 18, 2006

Should We Dismiss Evidence for the Hypothetical?

Sooner or later it was bound to happen - someone, somewhere would address the issue of economic factors if we abandon the decades old high carbohydrate, low fat recommendations. This month, in the American Journal of Clinical Nutrition, several Letters to the Editor appeared regarding the study by Weigle et al in July 2005, A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations.

For those who didn't read about the study last July - the researchers found that increasing protein in the diet to 30% of calories led to a spontaneous reduction in calorie intake, even when carbohydrate was constant, even with a reduction of fat intake, and resulted in significant weight loss when compared with a traditional macronutrient mix that provides 15% of calories from protein.

In their letter, Franco Contaldo and Fabrizio Pasanisi, write:

Weigle et al raise the intriguing question of whether high-protein diets are useful in preventing and treating excess body fat - a clinical issue that affects more than one billion people. They showed that a high protein intake reduces body weight by increasing satiety. Their study, together with the editorial by Astrup, raises the question of whether high-protein diets should be promoted in large numbers of people, particularly given the high protein intake typical of Western diets. Suffice it to note that the current estimated protein intake in the United States is already more than double the recommended amount. As a matter of fact, the human species is omnivorous and has developed very efficient adaptive physiologic mechanisms for fuel utilization, notwithstanding the feast or famine pendulum and that meat constituted the staple diet of our pre-Neolithic ancestors.

However, a meat-based diet - which has a high protein content - is largely less environmentally sustainable than is a vegetarian-based diet nowadays. A meat-based diet had little effect when the world's population numbered only a few million, unlike today when more than 6 billion individuals are competing for resources. Furthermore, a high-protein diet may have untoward effects, for example, on calcium and bone metabolism.

In conclusion, the findings reported by Weigle et al confirm some basic physiologic concepts of human nutrition; a high-protein diet can have untoward effects, may be difficult to adhere to, and, most importantly, is not environmentally sustainable. Thus, caution should be exercised in applying the findings of Weigle et al in the clinical setting.

Noteworthy here is that Cantaldo and Pasanisi actually admit in their letter than meat was the staple diet for our ancestors. They then move along to the logical reason to dismiss this - today we simply cannot sustain such a diet population-wide in the United States nor the world, and that such a diet would be an environmental nightmare and lead to competition for resources.

Since when do we ignore evidence and data that inconveniently impacts "policy"? Since when is our data, that supports a different macronutrient mix than we're recommending, have to be weighed against economic impact rather than health outcome?

Just who would be affected if we were to strictly use just evidence - not opinion, not feel-good policy making and not impacts the evidence might have - just the facts, just the data that relates to what really matters - our health. Well for one, we'd all be a heck of a lot healthier if we started to follow the science and not the opinions and entrenched dogma.

Let's put that aside for a moment though - Cantaldo and Pasanisi bring up something else that sounds so ominous...a higher protein diet won't just be an environmental nightmare, it would also untoward effects...on calcium and bone metabolism. They even provide references to show they have scientific evidence to support their contention!

Their choice of references is very, very interesting:

Eaton SB, Konner M. Paleolithic nutrition. A consideration of its nature and current implications. N Engl J Med 1985; 312: 283–9.
Kerstetter JE, O'Brien KO, Insogna KL. Low protein intake: the impact on calcium and bone homeostasis in humans. J Nutr 2003; 133(suppl): 855S–61S.

I doubt they thought anyone might actually read their references - both support a higher protein intake is not detrimental for health. Eaton et al provides insight that our ancestors diet included 30% of calories from protein; Kerstetter et al provides good data about the detrimental effect of low protein intake, specifically on bone and calcium!

In fact, Kerstetter et al states in their paper, "The long-term consequences of these low protein–induced changes in calcium metabolism are not known, but they could be detrimental to skeletal health. Several recent epidemiological studies demonstrate reduced bone density and increased rates of bone loss in individuals habitually consuming low protein diets."

To be clear, "low-protein" in their study was 0.7g protein/kg, the "high-protein" arms of the study consumed 1.0-2.1g protein/kg without detriment.

In their summary, they stated "There is agreement that diets moderate in protein (in the approximate range of 1.0 to 1.5 g protein/kg) are associated with normal calcium metabolism and presumably do not alter skeletal homeostasis."

Part of their reason for the letter to the editor was also Arne Astrup's editorial that accompanied the publication of the Weigel study findings that acknowledged a diet with higher protein has much potential to reverse the obesity epidemic we're in. In fact, he wrote, "The higher than usually recommended protein content of many popular diets, such as the Atkins Diet, The Zone, and The South Beach Diet, seems to point at possible solutions to the obesity epidemic. Many national dietary guidelines have, until recently, recommended that only 10–20% of the calorie content of the diet come from protein; however, 30–40% of the calorie content in the aforementioned diets comes from protein, at the expense of carbohydrates. Newer research indicates that the high-protein content of these diets may actually be the reason for their partial success in inducing weight loss, despite no restrictions in total calories."

In his rebuttal to Cantaldo and Pasanisi, however, he retreats slightly while trying to maintain some ground in support of higher protein diets, "In no way do I wish to suggest that overweight and obesity are "protein-deficiency conditions," but increasing the proportion of protein in the diet may be one way to attenuate the obesity problem in a sedentary population and, thereby, to help reduce many of the obesity-associated comorbidities. Current evidence from experimental and intervention studies suggests that an increase in the amount of energy provided by protein from the current 15–18% in most diets to 20–35% is associated with a spontaneous reduction in total energy intake and a weight loss of relevance for obese and diabetic subjects."

He adds, "In my editorial I mainly addressed the potential health benefits of increasing the proportion of dietary energy provided by protein at the expense of a reduction in fat and carbohydrate sources that are less satiating. I can only agree that many other issues need to be taken into account, such as safety aspects, economy, and environmental issues, before such recommendations should be made."

Quite frankly, dietary recommendations should not be based on anything but nutrition science, quality data and evidence. Yes, the environment in important. Yes our economy is important. And, yes, safety is also important. But, when scientists abandon the evidence and weigh in on what are policy issues, we no longer are guided by evidence, no longer committed to our mission of "evidence-based medicine" - instead, we're trapped by opinon and making decisions based on things not supported by the hard data.

This is dangerous territory for the scientific and medical communities - they risk ignoring their data to mold findings to meet politically correct opinions, long standing assumptions and economic policy. Researchers are not, and should not be charged with responsibility to solve all issues related to their findings, especially ones that impact the economy or environment. Such considerations are best left to the policy makers who are accountable to the public for economic stability and environmental sustainability.

The public deserves to have full disclosure of all the available evidence and not have its scientists carefully releasing only what is within current sustainability models or will not rock the economic boat. That's not science, that's manipulating things to fit the established paradigm and maintain the status quo - which, if you haven't noticed has made us fatter and sicker over the last three decades!

When our future health takes a backseat and our review of the evidence is held hostage to outside considerations that are not related to the data, we're in trouble. We've been doing this tap-dance since the early 70's and it's really time to stop and get back to the business of establishing dietary recommendations based on science, not economic consequences that remain hypothetical.

The alarmists who sound the warnings that we cannot sustain a higher protein diet - cannot feed ourselves such a diet let alone the entire world - and insist that such a shift would be disasterous to the environment fail to address the current situation where we're already depleting our soil and water resources, while at the same time contaminating our foods with pesticides and chemicals and already in an unsustainable situation!

If we're to get anywhere near establishing evidence-based nutritional standards, we're going to have to set aside concerns for the environment and economy and review the data on its own, without consideration for anything else but our long-term health and how our nutritional policy enhances or thwarts our health outcomes. If we do that, then we have a chance to really put together economic and environmental policies that will support and sustain us in the years to come. Trying to do it the other way around - that is molding the evidence to our current economic and environmental policies - is sheer madness without any hope of better health outcomes.

1 comment:

  1. Evidence-Based Sports Medicine (EBSM) - Torino Olympics 2006

    Citius, altius, fortius. The Olympic motto - faster, higher, stronger - is in full evidence in Torino. Whether on the ski-hill, skating oval or ice, the other aspect of the Olympic Games
    for some athletes is sports injury. As a medical librarian, I wondered whether evidence-based sports medicine (EBSM)
    (a relatively new field) was being practiced in Torino.