Friday, December 17, 2010

What’s the limiting factor?

Sometimes the “experts” get it wrong. Early in the 19th century, a school master declared a young man to be “hopelessly useless.” This pronouncement, coupled with a worrying interest in explosive fulminates, did not hint of the immense contribution he would make.

Justus von Liebig, circa 1850
from Wikipedia
Justus von Liebig (1803-1873) changed chemistry in Germany more significantly than any other chemist of his time and was responsible for the development of the teaching, research, and technology of modern chemistry. Forty-four Nobel laureates in Chemistry are scientific heirs of Liebig.

Liebig was one of the first chemists to organize a laboratory as we know it today. He improved organic and inorganic analysis of compounds. With Friedrich Wöhler, he developed a theory of radicals and made the first experimental discovery of isomerism. Liebig wrote books about agricultural and animal chemistry where there was a practical application of organic chemistry to animal and plant science.

Liebig’s Theory of Mineral Nutrients for Plants reformed agriculture during the mid 1800’s. This theory made the following major points:
  • plants take minerals up through their roots from the soil
  • soil is fertile only if nutrients removed by the plant are replaced
  • each kind of plant species requires different nutrients
  • one nutrient cannot substitute for another, which led to the “Law of the Minimum” 
The idea that plants take minerals up through their roots from the soil may not seem a great breakthrough, but we need to remember when this theory was formulated. Someday (hopefully soon!) the carbohydrate theory will be as readily accepted!

Liebig's Barrel
From here
Liebig’s “Law of the Minimum” in plant nutrition states that whichever nutrient is present in the least amount, relative to the requirement, will determine the yield of a plant. Liebeg used the image of a wooden barrel with staves of different lengths to illustrate this law. The effective volume (yield) of the barrel (crop) is determined by the shortest stave (limiting nutrient). Until that stave is increased, increasing the length of the other staves will, at best, be a poor investment. At worst, it may produce harmful effects (for example, nutrient toxicities).

Let’s apply this barrel analogy to a pasture-based livestock production system. I remember a visit to a pasture-based dairy farm in north western California. The farm’s pastures were subdivided into a number of smaller pastures, or paddocks. The farmer was concerned that the grass species he had planted were not persisting. He was renovating his pasture, by conventional tillage, on a five year rotation. “Perennial” pasture ought to last longer than five years!

As we walked across the paddocks, we saw that the grass-clover content increased from clover dominant (minimal grass) at the “head” of the paddock (where the animals are first turned in) to optimal in the middle, to grass dominant (with the grass too mature for dairy cow feed) at the far end of the paddock.

Each paddock had a single, fixed water source at the “head” of the paddock. These paddocks were managed, essentially, in a strip-grazing fashion. A portable fence would be set up ahead of the animals to give access to fresh feed. Each day the fence would be moved forward to provide a new grazing area. Each paddock would provide at least six days of grazing. Because of the fixed water supply, the animals could not be excluded from the previously grazed sections with a back fence and the animals would re-graze these sections. The grass at the head of the paddock was declining because it didn't have sufficient rest period after the initial grazing. The grass was dominant at the far end of the paddock because the cows preferred to remain closer to the water source and eat the higher quality herbage.

The majority of pasture Dry Matter (DM) yield is produced by the grass component. This farmer thought that his DM yield per acre (and therefore his milk fat production per acre) was limited either by the species (or varieties) of grasses he’d been planting, or by the fertility of soil in those pastures. He was prepared to pay a significant amount of money to address these conditions. In fact, the limiting factor was the lack of water in each grazing area. Given the costs of complete pasture renovation, the investment in improving the water supply system would produce the greatest economic return.

Now let’s apply Liebeg’s barrel analogy to human nutrition and health. The evidence indicates that the Standard American Diet (SAD) contains too much carbohydrate. Hyperinsulinemia (chronically elevated insulin) is a health problem for many. There are compelling, biologically plausible explanations for the more than 100 years of epidemiological observations strongly suggesting that highly refined carbohydrates are the most likely dietary cause of dyslipidemia, hypertension, heart disease, diabetes, obesity, cancer, Alzheimer’s disease, and other chronic diseases of civilization.

If a typical American, eating the SAD were to merely switch their meat sources to grass-finished ones, while the rest of their diet remained the same, how much health improvement could they expect? Probably not much, since the differences in meat due to feeding practices are NOT the limiting factors. These differences are real. They are quantifiable and they've been well documented. But they are not the short staves in this situation. Making an investment of money and effort here will not produce the best response.

Okay, how about if they were to switch to grass-finished meat AND only consume organic vegetables, grain products, sweeteners, and vegetable oils? Again, the evidence strongly suggests that they will NOT see the greatest “bang for their buck.” The short staves in thier diet are the grain products, sweeteners, and vegetable oils. Their elimination from the diet is more important than how they were produced. Organic "carbage" is still carbage!

It's hard to talk about this without being mis-understood. Nancy and I enjoy locally produced, grass-finished lamb (from Cattail Creek Lamb) and beef, and our pork comes from a local producer (Heritage Farms Northwest) who fatten their Red Wattle pigs on hazelnuts. Most of the vegatables we enjoy are locally produced and organic (and non-starchy!). We are making conscious decisions about supporting our local farmers. We are blessed to be able to afford to eat this way. And because we've eliminated grain products, sweetners and vegetable oils from our diet, we're more likely to realize the benefits from eating these wonderful foodstuffs. We've addressed the "short staves."


  1. Well stated. It's a tricky subject, but one that comes up often. You really do have to address the macronutrient content of the diet first, and then fine tune as you go.

  2. Nicely done Pete. I wonder if you've read "Meat: A Benign Extravagance" by Simon Fairlie, who makes the case for properly raised cattle and production of meat to feed populations. This, as you may know, is always the 'main' argument put forth to support why in this country mega feedlots are preferred instead of local, better managed, and more Earth friendly farms.


  3. FYF - Thank you. This is the argument I want to make when folks say that poor people cannot afford to eat a restricted carbohydrate type of diet. The evidence in fact shows that eating the low-priced conventionally-produced eggs, poultry, and hamburger as part of a diet that eliminates grain products, starchy veggies (potatoes), sweeteners and vegetable oils would produce tremendous benefits. As you say, fine tuning is a luxury that can be engaged in when one’s resources permits.

  4. Gabe - I haven't read Fairle’s book, but I’ll add it to my Holiday reading list. Thanks!

  5. What a sensible article this is... I was on a radio programme this morning saying the exact same thing. Today's obesity crisis is pretty much totally down to hyperinsulinemia, and the misery this little-understood phenomenon is causing people, bolstered almost entirely by the 'healthy eating' industry, makes my blood boil. How we would ever have evolved into an intelligent species if we'd fed our children on high PUFA/HFCS and a grain-based diet, is anyone's guess. Probably why our brains have shrunk since the advent of agriculture!!

  6. Thank you so much for this article! Most writers/bloggers seem to act like if you can't afford grass fed meat it's your fault! I always end up feeling bad even though my blood profile has improved significantly. I'm on a very small fixed retirement income and although I've done all the rest, including organic as much as my budget will allow, I still can't afford grass fed anything. I'm grateful to hear that I've addressed the short stave!!

  7. I'm glad I was able to ease your mind, grannymumentoog! Have you seen this list of the "Dirty Dozen" and the "Clean 15"?

    Pete B

  8. You are correct in your observations re Liebig's shorter staves analogy to nutrients and plant growth.

    I question the labelling of all ingredients or foods which contain CHO as a source of ill health, just because sugar (sucrose), HFCS and industrial flours are all CHO's. Root crops such as potato, yams and others all contain starch and yet have not been associated with the ill effects of these other items.

    I claim an interest: I grew up on an Irish farm, learned about crop rotation and clovers, ate lots of potatoes and butter - later KerryGold - and still do.

    There are many starchy foods which should not be "tarred with the brush" of those sweet saccharines.