by Loren Cordain, Ph.D.

Paleo Diet concept lies in its ability to simply uncover a pre-existing diet – a universal diet and dietary characteristics consumed by all humans until very recent times. The notion that omega 3 fatty acids promote health (as demonstrated in the scientific literature) is quite recent – as recent as the past 30 years. The notion that high protein diets may prevent disease and promote health and well being is newer still. Further, the recognition that dietary acid/base balance has anything to do with optimal health is barely in its infancy. Virtually, without exception, each and every one of these so-called nutritional “discoveries” in the scientific literature are treated cautiously, as if they were curious anomalies, rather than the predictable and highly probable findings that they actually are – had only the evolutionary template been employed.

In this and subsequent Paleo Diet Updates I will comment upon the latest scientific findings which increasingly lead to the inescapable conclusion that the evolutionary basis for human nutrition represents the grand unifying theory the discipline so sorely lacks.

Recent Scientific Findings: Acid/Base Balance

One of the major nutritional characteristics of ancestral human diets that have been almost totally ignored in both the lay and scientific literature is acid/base balance. Pick up the latest best selling diet book, be it a reincarnation of Dr. Atkins Diet Revolution, The South Beach Diet or whatever, and I can guarantee you that it will not even touch upon this crucial concept.

Briefly, let me review the basic concept. All foods upon digestion report to the kidney as acid, base or neutral. Acid yielding foods are all cereal grains, meats, cheeses, fish and salt. The only base yielding foods are fruits and vegetables1, 2. Fats, they typically displace base yielding fruits and vegetables, they are partially responsible for the net acid load in the typical western diet3, 4. There are a number of adverse health effects either partially or wholly caused by a net acid yielding diet including: osteoporosis, hypertension, stroke, calcium kidney stones, age-related muscle wasting, asthma and exercise-induced asthma2-6.

In the June issues of both the American Journal of Clinical Nutrition7 and the Journal of the American College of Nutrition8, two articles were published that reinforce the concept that net base yielding diets promote strong bones and may prevent bone mineral loss and osteoporosis.

Study #1

In the first article7, the authors report the osteoporosis preventing benefits of high intakes of fruit and vegetables in a cross sectional study of 125 girls and 132 boys between 16 and 18 years of age, 120 young women between 23 and 37 years of age, and 70 men and 73 women aged 60 to 83 years. Increasing consumption of fruits and vegetables were associated with greater whole body bone mineral densities in the boys and girls aged 16 to 18. In the older women 60 to 83 years of age, greater fruit intake was associated with a greater bone mineral content. No statistically significant associations were found in the younger women or older men between bone mineral measurements and consumption of vegetables alone.

Strengths: This study is rigorous for two reasons. First, actual weights of fruits and vegetables were assessed using a 7 day food diary and secondly bone mineral data were carefully adjusted for body size using dual energy X-ray absorptiometry (DEXA) machines. Without adjustment of body size, DEXA measurements may not truly be reflective of bone mineral content or density. In many dietary studies food intake is compiled not by daily diaries, but rather by 3 day recalls – a process which is notoriously inaccurate.

Weaknesses: This experiment is classified as a cross sectional epidemiological study. All epidemiological studies cannot show cause and effect between diet and disease, but rather only associations. Fruit and vegetable eating is associated with enhanced bone mineral status, but we cannot conclude from this epidemiological study that fruit and vegetable consumption causes greater bone mineral health. In New York City, there are always more fire trucks at bigger fires. Hence, more fire trucks are associated with bigger fires, but more fire trucks do not cause bigger fires.

Conclusions: As far as epidemiological studies go, this is a great one pointing in the direction that fruit and vegetable consumption may improve bone mineral status, but further, more powerful dietary interventions (in which fruits and vegetables are actually fed to humans and markers of bone mineral health are measured) will be required to make a stronger case.

Study #2

In the second article8 researchers led by Bess Dawson-Hughes at Tufts University in Boston conducted a dietary intervention in 40 healthy men and women over age 50. For 60 days, the subjects were put on either a high fruit and vegetable diet (base yielding) or an acid yielding diet in which cereals replaced fruits and vegetables. The subjects consuming the acid yielding cereal diet experienced increases in serum PTH (a hormone marker of increased bone breakdown), a loss of calcium in the urine and increased bone breakdown.

Strengths: In order to show cause and effect between diet and disease, scientists utilized 4 procedures: 1) epidemiological studies, 2) tissue or in vitro studies, 3) animal studies, and 4) human dietary interventions. When there are discrepancies among the various types of experiments, human dietary interventions represent the “trump card,” and these results prevail over the other procedures. This study represents the first long term (60 day) human dietary intervention demonstrating that an increased dietary acid load promotes changes in blood markers of bone breakdown.

Weaknesses: To conclusively demonstrate beyond a shadow of a doubt that net acid yielding diets promote bone mineral loss in humans, this same experiment should be carried out over a longer period (1 to 2 years) and actual changes in bone mineral content (as measured by dual x-ray absorptiometry [DEXA] machines) should be made, along with the blood markers of bone loss that were measured in this study.

Conclusions: The study represents the most powerful experiment to date showing that dietary acid/base balance is crucial for long term bone mineral health in humans. Despite this evidence, the notion of dietary acid/base balance has been completely ignored by the USDA in their My Pyramid Dietary Recommendations for the US public10 and by virtually all of the best selling diet books. Perhaps it is high time that the evolutionary basis for optimal human nutrition be incorporated as a key component when making public dietary recommendations.

Osteoporosis is a huge health problem world wide, afflicting 1 in 3 women and 1 in 10 men over the age of 55 years9. In the US 10 million Americans have osteoporosis, and costs are estimated at $17.9 billion annually9. Healthcare practitioners and the general public need to understand that there is more involved in the prevention of osteoporosis than just calcium intake and vitamin D.