What is a macronutrient?
Macro means large, in this case large in scale or quantity. In common usage, a macronutrient is a class of nutrient that is required in larger amounts – larger amounts than micronutrients like vitamins and trace minerals.
Sometimes the larger scale minerals - sodium, magnesium and calcium - are considered macronutrients or macrominerals. But usually we consider the caloric and structural molecules we need in large amount to be “the macronutrients”. They have for many years been classified by their chemical structure into three groups.
triacylglycerols - three fatty acids on a glycerol backbone. Used as fuel and for structure and function. Long chain saturated fatty acids (LCSFA) in particular are very energy dense, like diesel fuel for the body.
composed of simple sugars (CH2O)n, n>=3. Used as fuel and for structure.
Polypeptides – polymers composed of combinations of 20 different amino acids with highly variable side chains – Used for structure, function (enzymes) and for fuel as a back-up. The variability of the amino acid side chains makes for an almost infinite variety of protein shapes and functions – from a spider’s web stronger than steel to enzymes with highly specific functions.
For more than a hundred years, diets have been discussed with regard to their ratio of macronutrients, that is, whether they are composed of relatively more or fewer Carbs, Fat or Protein. In 2011, we are still arguing about the merit of diets that are called “high carb” or “low fat” or “low protein”, as if this was a very important, if not the most important dietary parameter.
Indeed C% + F% + Pro% = 100%
But so what?
This is appealing at a crude level, as certainly for parts of modern history, and in researching metabolism, it is interesting to learn how we can manipulate macronutrient ratios and what effect this has, especially at the extremes. The effects we see from manipulating them, like with a low carbohydrate diet, certainly reinforce the impression that macronutrient ratios are very important. And the lipid hypothesis, both to those who buy it and those who think it’s nonsense, forces us to take positions on either side of a “low fat/high fat” axis.
But I would like to suggest that the whole concept of macronutrient, like that of the calorie, is determining our language game in such a way that the conversation is not making much sense.
I think we are stuck in a 20th century dietary paradigmatic purgatory, and we could move to a more fruitful one by speaking less of macronutrients, or at least coming up with a new taxonomy for them.
My reading of paleoanthropology and ethology of modern hunter-gatherers suggests that it may have been possible to eat healthy and avoid diseases of civilization (including accidental weight gain) with no concept whatever of macronutrients. Are there words for protein or fat or carbohydrate amongst the Hadza or the !Kung San or the Native Sioux or the Kitavans in their native languages? I am sure there are words for fish and cassava and meat and such. Do they have discussions about how to apportion their calories among these? And how did they and every other animal on the planet and the entire ancestral hominid lineage manage without calculators and scales?
Approaching from the other end, looking at what we know about food science with just moderate sophistication, of what use is the concept of "macronutrient" now?
Let’s look at fats first.
Is “high fat” good or bad? Are “fats” good, bad or neutral?
Don’t we know enough now to ask “which fats”?
Under the rubric of “fat” we have the perfect human fuels – what I call #1 Diesel – long chain saturated fatty acids (LCSFA) like Myristic (C14), palmitic (C16) and Stearic (C18) acid as found in the milk and meat of ruminants. These are, by no coincidence, the same saturated fatty acids we humans use to store energy in our own bodies – our own internal #1 Diesel. As far as I can tell, there is no limit to the amount of this kind of fat that you can eat, as long as your protein and micronutrient needs are being met. You cannot eat “too much” saturated fat unless you are not getting enough of something else. This is just the principle of displacement, though, and has nothing to do with any toxicity of these fats as food. Of course, these LCSFAs are the very fats that, in the bizarro-world of conventional nutritional wisdom, are supposedly the most dangerous and cause heart disease and cancer. That there is no real evidence for this belief, and that LCSFA are actually one of the most healthful sources of caloric fuel, is what makes embracing them and rejecting the lipid hypothesis the lodestar of PaNu or any rational approach to diet. You can’t take the most important step in improving your diet until you do this.
Stearic Acid – #1 Diesel for the human body
An incommensurable dilemma presents a binary choice where both choices cannot be correct. It is often the crux of establishing a new paradigm. A good example of an incommensurable is the Ptolemaic vs the heliocentric model of the solar system. Not all incommensurable dilemmas are solvable by accepting one or the other paradigm. Sometimes the question is framed wrong or the language is defective – that is what I am suggesting in the case of “low fat vs low carb” – the framework of the dilemma itself is wrong – so to move to a more workable paradigm requires asking a different question with new language.
In the larger case of how to eat healthy in a manner supported by medicine and evolutionary science, the truth value of the lipid hypothesis is the incommensurable dilemma. You simply have to choose whether it is true or not. You really cannot avoid the question. If you hedge, you end up running into nonsense like being “low fat” and “low carb” at the same time. You may end up terrified of both saturated fat and starch and then you’ve made no progress at all, as you really should not be afraid of either one*!
I believe dealing with the incommensurable dilemma of the lipid hypothesis is far more important than using any kind of evolutionary reasoning or being at all “paleo”. If you can’t make the crux move, with all there is riding on it culturally (all the terrible public health consequences), and all the evidence laid out for you, there is no point in going in more speculative directions, like “what did paleo man eat?”. This is partly why “paleo” on my blog now means just old or ancient, instead of Paleolithic – with all the speculative and unknowable baggage that reference to the Paleolithic carries.
Next we have so-called medium chain triglycerides (MCT). These are saturated fats with fatty acids that have a chain length of 6 to 12. They are found in coconut and mother’s milk and have some interesting properties. Even though they are saturated and quite similar to LCSFAs, they are metabolized differently. They do not require bile acids for digestion, and they go directly to the liver via the portal vein. They seem to undergo obligate metabolic processing that results in ketone bodies – so they will enhance the level of ketosis (ketones in the blood) even without eating a VLC ketogenic diet. They can be good fuel sources, but in addition may prove useful in a therapeutic context by enhancing ketosis.
Next, consider n-6 polyunsaturated fatty acids or n-6 PUFA. The principal of these is Linoleic acid – the Third Horseman (of the dietary apocalypse, one of our three Neolithic Agents of Disease).
The formula is 18:2 n-6. There are two unsaturated, reactive, oxidizable double bonds, with the first found at the 6 position. Linoliec acid (LA) is an essential fatty acid. We must have some in our diets, as we can’t make it ourselves. However, since the introduction of plant and seed oils into our diets as food as a by-product of industrial extraction techniques that were impossible before the machine age, the western diet has seen quantities of LA that are often nearly an order of magnitude greater than what humans or hominin ancestors could have ever experienced. A healthy level of LA might be as much as 2-3% of total calories. Intakes in north america on the SAD may be as high as 10% or more. Excess linoleic acid alters the tissue 6:3 ratio which in turn affects inflammation and the immune system, encourages a thrombotic state, may cause cancer, may interfere with leptin signaling in the brain, may affect gut permeability, may be hepatotoxic, may contribute to oxidative damage affecting the development of atherosclerosis and through a variety of mechanisms, including affecting insulin sensitivity, may contribute to metabolic syndrome and obesity. The amounts in our diet are far outside of any reasonably likely evolutionary experience and even though LA is essential and LCSFAs are not, it would be fair to consider LA a metabolic poison when getting 10% of calories from it. A bad fat indeed.
Again, we should note that many standard bearers of the reigning paradigm consider LA a “good fat” - having almost medicinal properties against heart disease. As there is no direct evidence for this, their belief only makes sense once you realize that this is because replacing LCSFAs in the diet with LA “improves” LDL numbers. So their faith in the lipid hypothesis essentially compels them to believe that the worst naturally occurring fat you can eat is a “good fat”. Do you see now why confronting the lipid hypothesis is your crux move in sorting out the science of diet?
The next fats to consider are the long chain n-3 PUFAs Docosahexanoic acid (DHA) and Eicosapentanoic acid (EPA). These are polyunsaturated fats that are only obtainable in quantity in animal products like fish and grass-finished ruminants.
The 6:3 ratio in plants should be ignored. Nuts or seeds that have any n-3 at all should be thought of only as sources of unwanted PUFA. The n-3 they contain is not converted to the useful long chain n-3s we need at a high enough rate to even consider them food. Plant n-3s like alpha-linolenic acid (ALA) from flaxseed oil should just be considered sources of excess total PUFA like LA, only even more likely to cause oxidative damage as they have more double bonds and are less heat-stable! Plant oils like linseed oil (contains ALA) are literally varnish. I use them to make furniture. I use them for oil paintings as a medium. I avoid eating them.
DHA/EPA are found in pastured butter, beef and lamb, and fatty fish. These are the n-3s that balance the n-6s and that determine the denominator of our 6:3 ratio. As I’ve said before, your total PUFA should be no more than 4% of calories and your 6:3 ratio no higher than 3:1, preferably less than 2:1. You will not achieve this if you eat a lot of chicken or handfuls of nuts. If a person has unavoidably high n-6 in the diet, then adding some DHA/EPA is a good idea. The higher the total PUFA above 4%, the more benefit to supplemental EPA/DHA. So n-3 PUFA is a good fat if you need it, but once your 6:3 ratio is OK, it becomes a bad fat, as it is even more unstable and reactive in your body than n-6 LA, as it has more double bonds. So here we have a fat whose goodness is entirely contextual, depending on the rest of the diet (consumption of n-6) and even the present status of tissue saturation by n-6 due to dietary history.
Note: One might accelerate the normalization of the 6:3 ratio by supplementing beyond the calculated requirement for a year or so, but I would not exceed the required ratio by more than an extra gram or so of DHA/EPA combined.
Finally, we can consider the dreaded trans fats. A trans fat is a triglyceride where the fatty acid is unsaturated – it has at least one double bond, and the carbon atoms on either side of the double bond have hydrogen atoms on opposite sides. This makes the shape of the molecule similar to a saturated fat, so that it is more-or-less straight, like this:
This is Elaidic acid, the principle trans fat in hydrogenated veggie oils.
For comparison, here is oleic acid, which is found in beef fat and olive oil, and is considered to be relatively healthy (by those on both sides of the lipid hypothesis divide, interestingly enough). The only difference is the orientation of the hydrogen atoms that were added, and this results in a bend for oleic acid versus the straighter configuration of Elaidic acid.
The effect the bend has is to lower the melting point of the fat, as the bend makes it harder for the molecules to fit tightly together where Van Der Waals forces between the atoms make the structure more crystalline or solid.
Now we should make it clear that there are trans fats found in nature. They can be up to a few percent (usually 2%) of the fat in the meat of ruminants and in dairy fats. However, the predominant type of natural trans fats are conjugated linoleic acid (CLA), otherwise known as rumenic acid, and its precursor vaccenic acid. Vaccenic acid (C18:1 trans-11) can be converted to CLA by humans, which is not only proposed likely free of the negative metabolic effects of the dominant artificial trans fats (like Elaidic acid), but possibly has anti-cancer properties. Both of these “good trans fats” are made by bacteria in the stomach of ruminants, and like the long chain n-3 PUFAs we like, they are made in greater amounts on a grass-only diet. So grass-finished ruminant milk products and fatty meat will have these good trans fats, and they are good for us.
So why are there artificial trans fats and why are they bad?
This Wikipedia article gives a good account of the history, but briefly, artificial trans fats were first introduced as a result of attempts to process waste industrial vegetable oils (soy, cotton seed) into something resembling animal fats like butter and lard. Because oils rich in n-6 are rather soupy at room temperature (those kinks from the -cis configuration), they can be hydrogenated in order to behave more like saturated animal fats in the kitchen and in baking. This is achieved by adding hydrogen at the double bonds – hydrogenation. If there is complete hydrogenation – say oleic acid is completely saturated to C18 stearic acid – this is not a problem as you have just made a tasty saturated fat. But partial hydrogenation – say, turning a PUFA into a MUFA with a single double bond – will create these artificial trans fats. The catalyst for the reaction is indiscriminate and will create roughly half –cis configuration and roughly half –trans. The cis are not likely a problem, but -trans fats resulting from hydrogenation of something that started out chock-full of linoleic acid -like cottonseed or soy or corn oil - will go from 0 to 25% or more.
Artificial trans fats have been linked to variety of metabolic disturbances. Read Mary Enig’s book Know Your Fats for a good summary. Some of these are based on effects on supposed surrogate markers for atherosclerosis like LDL and HDL, which of course makes me a bit skeptical, but even with no direct human evidence of mortality, they should not be eaten, as they have simply never been part of the human diet. (I am perfectly comfortable proscribing substances that are literally not food, even on weak evidence)
Before the beginning of the 20th century, butter and lard were king. After mid century, replacement of animal fats with cheap industrial oils and margarines meant our diets had almost as much artificial trans fats as saturated fats in them. Remember this when looking at literature indicting saturated fat, as for much of the 20th century they were often lumped together in studies looking at fat in the diet.
Nowadays, trans fats are of less concern, as they are limited by law to no more than 7% of total fats by removing the -trans isomers and leaving the -cis ones, and even Crisco is now relatively low in them. The easy way to avoid them is to totally avoid anything with “partially hydrogenated vegetable oil” in it – even if they claim a low trans fat content. Better yet, completely avoid all industrial vegetable oils –they all have too much n-6, even olive oil.
So in summary, we have added two more subclasses of fats, natural trans fats –naturally occurring vaccenic and rumenic acid, and artificial trans fats – chiefly Elaidic acid. One class is very good and the other is very bad.
We can tally these up now and even create some more food-relevant subcategories:
A New fat Taxonomy
LCSFA - long chain saturated fatty acids - best
Monunsaturates - Oleic acid from animal fats and olive oil - good
n-6 PUFA - Technically essential but in huge excess due to technology - bad
n-3 PUFA - necessary to balance excess n-6 but otherwise bad - contextual
MCT - Medium chain saturated fats - good in reasonable amounts
NTF - Natural trans fats like vaccenic and rumenic acid - good
ATF - Artificial trans fats like Elaidic acid -not found in nature - bad
The preceding would be the chemically based, "nutritionist" taxonomy. But we can construct a real-food based taxonomy by recombining the nutritionist elements into a 6 part scheme like this...
Grass finished ruminant animal fats. LCSFA and Mono in roughly equal amounts. Same small amounts of n-6 as IRAF, but more n-3 to balance. More NTF. Best.
Industrial grain-fed ruminant animal fats - LCSFA and Monounsaturates in roughly equal amounts with smaller amounts of PUFA - may be deficient in n-3 PUFA. Has less NTF. good
Non-ruminant animal fat. Highly variable. Has LCSFA but may be very high in n-6 and if grain fed poor in n-3. More sensitive to diet of the animal than IRAF or GRAF. fair if pastured but poor otherwise. Think factory chicken.
Temperate plant oils. Artificially abundant due to technology. excess n-6, effectively no n- 3. Some MUFA. Little LCSFA bad
Tropical Plant Oils. Coconut and Palm oils. Good source of MCT and/or LCSFA - lower in n-6 and n-3. These are also made available by processing technology, but their content is better than TemPO. Good.
Frankenfats. TemPO chemically modified by hydrogenation. Very bad - avoid completely.
I hope I have convinced you that the macronutrient label of "fat" as in "high fat" is or "low fat" diet is metabolically not very useful. Keep this in mind when you read anything at all in the literature about "fat".
Perhaps you can help me change the nutritional language game by using my new fat taxonomy and resisting the old one, even if you disagree with my judgements about their nutritional merit.
When you discuss diets or ways of eating, you can use language like "I eat PaNu, a high GRAF, low TemPO diet".
Or, "PaNu is a high GRAF, low TemPO, low NRAF, zero FF way of eating". PaNu is "low fat" in regard to TemPO and n-6 PUFA, but very high fat in regard to LCSFA, Mono and GRAF.
Or "Dr. Davis advocates a diet free of wheat, but unlike PaNu it is low GRAF and IRAF, but high TemPO and high n-6 PUFA". Davis is "low fat" in terms of animal fats, but "very high fat" in terms of n-6 PUFA.
We'll deal with "Carbohydrates" and offer a new taxonomy for them in Part II.