Mark sent me a .pdf of a very interesting paper the other day: "Nitrogen and Food Production: Proteins for Human Diets," V. Smil, Ambio vol 31 no 2, March 2002. It got me thinking about lower-carb living and sustainability.
One way to think about farming: "[A]griculture's principal objective is the production of digestible [nitrogen]." Nitrogen is a proxy for protein, and its availability in the soil limits how much protein can be produced from the land. That's why the advent of ammonia fertilizer led to such an explosion in land productivity. But nitrogen fertilizers have environmental costs, and so we want to use them efficiently.
Back when I was trying to live low-carb, Atkins-style, one of the things that troubled me about it was that it seemed so... gratuitously meaty. The Atkins folks are now recommending "at least 4 to 6 ounces of protein foods per meal," "8 ounces... if you're a tall guy," but five or six years ago I had gotten the distinct impression that you were supposed to eat "as much as you want" of bacon and beef and the like.
Basically, the impression was: Replace your bread, rice, and pasta with meat, eggs, and cheese. Right? And of course, even now, six ounces of protein-based foods per meal is more than a pound a day. You've got to eat something, right? And you don't want to be hungry? And carbs are out? So high-protein must be in.
But of course this is far more protein than individuals need. Protein can't be stored,* so eating extra is wasted. It's greedy, too, on a societal and environmental level; Americans overeat it, and pour nitrogen fertilizers into the soil in order to overproduce it, while in other parts of the world demand outstrips supply.
So why is the Atkins recommendation so high? I think it's because the Atkins diet sells itself with that "you can eat as much as you want" theory. The extra meat will fill your plate and your stomach, be satisfying to chew, and taste good; it is made of "normal" stuff that you're used to eating; and if the research on insulin resistance is to be believed, it won't contribute to your fatness. You can, indeed, lose weight while eating lots of Atkins hamburger salads.
But it's still wasteful, if you're eating more protein than your body needs. And the more people in affluent nations who try to fix their fatness by following Atkins-style high-meat low-carb, the more overall global demand for meat rises -- and for already-overnourished nations like us, that's shameful.
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This is one reason why, even if we concede that high-refined-carb diets cause obesity and low-carb diets can cure it, we still have a gluttony problem. A pound and a half of meat every day is a ridiculous amount of meat to eat, even for a "tall guy."
Let's concede that a small number of obese, insulin-resistant people will not respond to a diet unless it contains virtually no carbohydrates at all. These few folks will need a diet that's almost all protein and fat, of necessity based mostly on animal products. They want to eat reasonably-sized meals with enough calories in them that they don't suffer terribly. Okay, let those few people subsist on mostly meat, and more meat than their protein requirements call for. Chalk it up as an expensive medical treatment. But it's terribly wasteful to start there as a first resort for weight loss, or worse, for a lifelong way of eating.
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Here are some things to keep in mind when designing a lower-carb, but more-sustainable way of eating.
1. Too much protein and too little fat is an important cause of the famous constellation of side effects that accompany "Atkins-style" low-carb eating.
From Gary Taubes, Why We Get Fat, pg 214-216:
This shift [from running on carbohydrates to running on fat] can come with side effects. These can include weakness, fatigue, nausea, dehydration, diarrhea, constipation, [postural hypotension], and the exacerbation of pre-existing gout. ... This reaction is why some who try carbohydrate restriction give it up quickly.
...The reason for the side effects now appears to be clear, and physicians who prescribe carbohydrate restriction say they can be treated and prevented. These symptoms have nothing to do with the high fat content of the diet. Rather, they appear to be a consequence of either eating too much protein and too little fat, of attempting strenuous exercise without taking the time to adapt to the diet, or... a web of compensatory responses [from the beneficial drop in insulin levels] that can lead to water retention and what are called electrolyte imbalances.
So too much protein is one cause of the unpleasant side effects. Eat more fat and less protein -- which means you can eat less animal product and more vegetable oils like coconut, avocado, olive -- and the lower-carb adventure might feel a whole lot better. (Meanwhile, make sure you get enough salt and don't overdo the exercise).
2. Don't overestimate your daily protein requirements. Three grams for every ten pounds of body weight is slightly more than you probably need -- a number I get from using the recommendation of (0.6 g protein)/(kg body weight)*. Another way to think about it is one gram per ten pounds of body weight at each of your three meals.
I weigh 113, so it's doubtful I really need more than 34 grams of protein per day. Let's be generous and call it 36: 12 grams of protein at each of breakfast, lunch, and dinner. So at each meal I can get enough protein from:
- 2 eggs; or
- 0ne-third of a small (5 oz) can of tuna; or
- one smallish chicken thigh; or
- less than 3 ounces of not-particularly-lean ground beef; or
- almost two ounces of cheddar cheese; or
- a cup and a half of whole milk or yogurt.
Now, if I got most of my protein from plant sources like beans and grains, I might need to eat more, because the body uses the protein in these less efficiently. And mind you, I don't weigh very much. If you weigh 250 pounds, you might need twice what I need. Oh, and growing children and pregnant women will need more than this. So will someone who does a lot of heavy lifting. But the point is, if low-carb living means you're going to eat globally-scarce animal protein at most meals, you don't have to consume more than your "fair" share (unless it turns out you have a medical need for it).
3. Fill the rest of the plate with nutritious vegetables. Flavor them with enough butter, sauce, oil, or cream to give you plenty of energy. If you want a low-carb, moderate-protein diet, logically you must eat a good deal of fat. There is nothing wrong with this. And the thing that will give it to you, along with a nice lengthy eating experience and a sensation of fullness, is the dressed vegetable side dish. Eat your veggies, and eat them with plenty of tasty, tasty fat -- not an excess, but enough to give you your daily calories. This fat need not come from animal products. The bulk of your calories can thereby come from veggies.
Atkins-style low-carb set an initial upper limit on even salad vegetables, which naturally means the dieters felt they had to eat more meat just to fill up their plates. Some people might need such drastic limits, but I'm betting that most people will do fine eating as much broccoli, okra, cabbage, spinach, collards, cucumbers, cauliflower, asparagus, and the like as they want. Might as well give it a try.
4. Don't waste so damn much food, especially protein. Here is a sad statistic: Somewhere between 25 and 55 percent of the food available to people living in North America, Oceania and Europe is simply wasted.* Thirty-six hundred calories* are available to every American every day; that doesn't count exports. We eat too much to begin with, and what we don't eat we waste.
- A lot of these calories are wasted by retail sellers, who have to throw out expired meat and the like.
- A huge amount is wasted by the restaurant industry; I don't know this, but I suspect that the fancier they are (i.e. the more operating expense they can pass on to the clientele), the more wasteful.
- But we also waste a lot of food at the household level, by buying too much and cooking too much in the first place, by over-trimming, and generally by being too picky.
I've made this point before: The first place you can reduce your carbon footprint is by wasting less so you can buy less. What's more, unlike many other ways to go green, you'll actually spend less money (and maybe even time) on the effort. (A somewhat frightening implication here is that every time we eat in a nice restaurant, we necessarily contribute to the problem. Don't really want to go there....)
5. Choose animal products that make efficient use of protein. One way to compare protein sources is by feed protein to food protein conversion efficiency. We could get protein by eating cereals and legumes; or we could feed some of the cereals and legumes to animals, and then eat the animals. How much of the protein in those cereals and legumes can you get back? We can accept a less-than-100-percent conversion because animal proteins are more bioavailable to us, and also because they come with valuable fats, nutrients, and iron (not to mention that most of us like to eat animals). But how good can it get?
According to Smil, the best you can do is dairy products, which give you back 40 percent of the nitrogen (a proxy for protein) you fed to your cow. Aquacultured fish are next, tied with eggs at 30 percent efficiency. Eating chickens gives you back about 25 percent of what you "spent" in feed protein. Pork: only 13 percent. And when you get to beef cattle, it's pretty abysmal: five percent.
It does depend quite a bit on how your beef is raised:
Beef production is inherently the least efficient way of supplying dietary protein through animal feeding. ... This inefficiency is irrelevant in broader [nitrogen] terms as long as the animals are totally grass-fed, or raised primarily on crop and food processing residues (ranging from straw to bran, and from oilseed cakes to grapefruit rinds) that are indigestible or unpalatable by nonruminant species. Such cattle feeding calls for no, or minimal—because some pastures are fertilized—additional inputs of fertilizer-[nitrogen]. Any society that would put a premium on reducing [nitrogen] losses in agroecosystems would thus produce only those 2 kinds of beef. In contrast, beef production has the greatest impact on overall [nitrogen] use when the animals are fed only concentrates, now typically mixtures of cereal grains (mostly corn) and soybeans.
Switching from conventionally raised beef to grass-fed beef is expensive, and not even practically possible depending on the grocery options where you live. But switching some of your conventional pork and beef consumption even to ordinary eggs and dairy is a cheap change, available to anyone anywhere, that can halve your meal's nitrogen footprint while still providing you high-quality protein, enough to support even a quite low-carb diet.
*Asterisked information comes from the Smil paper.