New Under the Sun:
Volume 3, Issue 12
Once again, another year comes to a close. In this season of short, often cloudy days, it is important to focus on light. Make sure your day is as full of light, natural or artificial, as possible. You will feel happier and be more likely to stay with a healthy lifestyle. May your holiday season be filled with light and happiness.
Fruits, and Veggies, Good Health, Oh, My!: Several studies have recently been published touting the benefits of fruits and green leafy vegetables. The studies discussed here focus on bone health. An observational study conducted in Ireland of 1,345 adolescents aged 12 to 15 found that those girls aged 12 who had the highest fruit consumption also had the highest bone mineral density as measured at the heel. There was no such correlation observed among the older girls or among the boys in either age group. There was also no correlation observed with vegetable intake. However, the authors noted that these adolescents ate very few vegetables and only about half the daily recommended fruit intake. A large number of possible confounding factors such as height, weight, smoking, alcohol use, puberty status, supplement use, social class, and activity levels were taken into consideration. The correlation between fruit intake and bone density held. McGartland CP, Robson PJ, Murray LJ, Cran GW, Savage MJ, Watkins DC, Rooney MM, Boreham CA. Fruit and vegetable consumption and bone mineral density: the Northern Ireland Young Hearts Project. Am J Clin Nutr. 2004 Oct;80(4):1019-23.
Another study conducted in the United States provides support for this correlation. Fifty-six girls were divided into two groups based on their fruit and vegetable consumption: those who ate less than three servings per day, and those who ate more than three servings per day. Once adjustments were made for body mass, age, and activity levels, those girls in the high intake group were found to have the highest total body and radial bone areas. This was probably due to the fact that they also had the lowest levels of urinary calcium excretion. Tylavsky FA, Holliday K, Danish R, Womack C, Norwood J, Carbone L. Fruit and vegetable intakes are an independent predictor of bone size in early pubertal children. Am J Clin Nutr. 2004 Feb;79(2):311-7.
The probable reason for the correlation is that an acid-forming diet leaches minerals from bones, reducing their density. Fruit and vegetables are alkaline-forming foods which serve to balance the acid-forming foods, thus reducing bone mineral loss and maintaining bone density. For an excellent overview of this issue, see Dr. New’s article cited below. One of the points discussed in her article is the fact that the reason many vegetarians do not maintain good bone mass as they age is that their diets are heavily grain and cheese based. It may be that their intake of fruits and green, leafy vegetables is inadequate to counter that high-acid diet. In another case cited by Dr. New, raising the intake of fruits and vegetables from 3.6 servings per day to 9.5 resulted in a significant decrease in excretion of urinary calcium from 157 mg per day to 110 mg per day. Overall, the conclusion from this article appears to be that the lower the acid content of the diet, the better the individual’s bone health is. New SA. Intake of fruit and vegetables: implications for bone health. Proc Nutr Soc. 2003 Nov;62(4):889-99.
Comment: For more information on which foods are alkaline-forming and which acid-forming, click here for a chart: http://www.thewolfeclinic.com/acidalkfoods.html It is interesting to note that milk and milk products, touted by the dairy industry as a great source of calcium, are among the acid-forming foods. The implication of this is that the calcium in these sources will probably be inadequately utilized. In fact, the majority may end up being excreted unless the diet also includes a very high percentage of fruits and vegetables. Such a high fruit and vegetable diet, along with adequate UVB radiation to provide optimal vitamin D levels, may be why our ancient ancestors could maintain skeletal health despite a low calcium intake. It may also explain the otherwise counter-intuitive finding that the highest rates of osteoporosis are among those northern European populations and their descendants who have the highest intake of dairy foods.
These Legs are Made for Walking: Speaking of bones, Lieberman and Bramble published research in a recent issue of Nature which implies that the human physique, particularly the lower body, is uniquely shaped for long distance running. In effect, they say that running made us human. This is an intriguing idea and they offer a number of reasons in support of their proposition. However, before we ran on two legs, we needed to develop the trait of walking on two legs.
Bipedality, walking on two legs, dates back at least 4.5 million years. Once movement on two legs became the favored locomotive method of these early primates, they made the taxonomic transition from being a type of ape to being a type of hominid and, thereby, became our ancestors. The bodies of these early hominids, and by extension, our own, are extremely well-adapted for steady, although relatively slow, walking. It is my own view that bipedality evolved for foraging for waterfowl eggs and shellfish, along with various plants, in the marshy edges of streams and lakes. Speed was not of the essence, but a vertical posture was, especially for females with infants.
Whatever the reason for the origins of bipedality, Bramble and Lieberman posit that around 2 million years ago, with the transition from Australopithecine to Homo, some factor caused these hominids to change from long distance walkers to long distance runners. The evidence they marshal in support of this involves changes found in Homo, but not Australopithecines and includes, but is not limited to: a nuchal ligament (a band of tissue firmly connecting the back of the head to the spine); wide knee joints; Achilles tendons that act as springs; heat-dissipating sweat; and large gluteal muscles. The authors conclude that the only reason for these adaptations is to provide us with the ability to run long distances effectively and that these traits evolved so that we could be more efficient scavengers on the African savannah. Or, perhaps it was so that we could run our prey into the ground by being better endurance runners than they were. Or maybe it was both.
There are several problems with this hypothesis, but I will deal here with only two. The first is that running leads to about six times as many injuries as does walking. See this month’s Tip below. An injured hominid was pretty quickly a dead hominid. The second is that it seems improbable that a hominid female saddled with a young child and a nursing infant (the probable condition of any pre-20th century female of child-bearing age) would have any use for endurance running. Once again, male researchers have taken their own interests (both authors are long distance runners) and, ignoring the facts of life of females encumbered by offspring (and these would be the only females who passed on their genes and their traits), have proposed a hypothesis of extremely limited utility. Bramble D. M., Lieberman D. E., Born to Run? Nature, 432. 345 - 352 (2004).
AnthroHealth Tip of the Month: Walk, don’t run. Despite Lieberman and Bramble’s assertions that humans are designed to be long distance runners, this is not an appropriate form of exercise for most of us. Runners are far more likely to sustain injuries while running than walkers are while walking. A study in the American Journal of Sports Medicine found that runners sustained about 11 injuries per 1000 hours of activity compared to the 2 injuries per 1000 hours for walkers. To put this into perspective, squash and basketball players sustain about 14 injuries per 1000 hours of activity, while Alpine skiers sustain 8 injuries per 1000 hours. Because our bodies are capable of an activity does not mean that this is an activity we were “designed” for or “meant” to do, especially if it results in a fairly high rate of injuries. So, make the most of a sunny winter day and enjoy a pleasant, brisk walk. And eat an apple while you walk for an added benefit to your bones. 'Injuries in Recreational Adult Fitness Activities,' The American Journal of Sports Medicine, vol. 21 (3), pp. 461-467, 1993.
© 2001-2009 Kathleen E. Fuller, PhD. All rights reserved.