ETA: I started a bounty on this question because I never found the definitive answer I was seeking. Links/studies cited to answer the question below should assist nursing paleo moms in terms of their knowledge of how their fat consumption affects their babies for better or for worse. (On a personal note, despite wanting to lose baby weight I waited until breastmilk wasn't the main component of my daughter's diet before going into longer term ketosis because I wasn't sure if it was potentially harmful to an infant who consumed only mother's milk.) Bonus points if ketogenic/very high fat diets in mothers (and effects on their nurslings) can be addressed in your answer.
This question has been bubbling on the back burner of my mind over the past few days. It has piqued my curiosity because I am a nursing mother whose 9-month-old baby (like her mama) loves to sample bits of fat-sauteed veggies, grass-fed butter, 85% lean grass-finished ground beef, eggs, and other fatty delights. In other words - I have a vested interest in feeling certain that saturated fat is an integral, beneficial part of feeding my baby.
I have read that human breastmilk's fat content modulates based on the fat type/profile in the diet of the mother. (see links at bottom)
I'm pretty sure that I have also recently read in a couple of primal / paleo blogs that in grain-fed cows, there is some mechanism by which the mother cow's milk is forced to have as high as physiologically possible Omega-3 content, despite all dietary indicators that the milk's O-3/O-6 ratio should be driven by grain-driven Omega-6s. In other words, the mother cow's milk indicates a sacrifice on the part of the mother cow's Omega-6-riddled body to produce the milk that is closest to a grass-fed standard as is possible because it "knows" that the baby calf actually needs a higher Omega-3/Omega-6 ratio than what the grain-based diet would tend to generate. (If anybody knows of some links/blog posts/articles illustrating this concept, please feel free to post in a comment as I've been trying to retrace my steps with no luck yet.)
So I guess this leaves me with a question:
If there is a mechanism in cows by which the milk is still pushed to the optimal nutrition profile as allowable because of OR in spite of the diet - AND there could be (pure speculation on my part here) a similar mechanism (or set of mechanisms) in human lactogenesis to compensate for maternal nutritional deficiencies, why does the fat profile/content in human milk vary from one mother to another (reflecting differences in diet)? In other words, wouldn't the fat profile/content of a human mother's breast milk not modulate as much if it were so critical to the nursing infant - wouldn't even a vegan or low-fat-diet mother's milk still come out with a surprisingly high saturated fat profile, even at the expense of such mothers' bodies?
Or am I comparing apples and oranges (and berries and kiwis) re: resulting O-3/O-6 ratios v. resulting saturated fat content (not to mention cows v. humans?)? I've been going around and around with it in my head for a few days and wanted to ping PaleoHackers' collective wisdom and analysis skills.
Some interesting and at least tangentially related studies that could fuel the discussion:
- Human Breastmilk Saturated Fat/Cholesterol content increases at over one year of lactation
- Fatty acid composition of human milk from South African black mothers consuming a traditional maize diet.
- Breastfeeding: Unraveling the Mysteries of Mother's Milk "...[breast milk's] fat composition is markedly affected by the maternal diet."
asked byfamilygrokumentarian (12179)
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on September 17, 2010
at 02:41 AM
Here's something for the discussion. It's fascinating, although may not be a direct answer to your question. Stephan on linoleic acid in breast milk from one generation to the next:
on April 08, 2011
at 09:08 PM
Hi, Familygrok. I've spent some time looking into this and here's what I've come up with.
OK, it seems like the majority of the stuff you'll find on diet and breast milk is about PUFAs. A lot is about the so-called essential PUFAs: ALA (alpha linolenic acid, 18:3 n3, the one in flax seed) and linoleic acid (18:2 n6; this is of course one of the three horsemen but technically speaking it's essential because the body can't manufacture it itself). The former is the one we're more interested because it leads to DHA. But of course we're skeptical about the amount of conversion there is from ALA to DHA. So are these researchers; thus a lot of the studies are about DHA also.
There are a lot of vague statements out there on breast milk compostion that seem to want to have things both ways. For example:
Lipids are the most variable constituent in human milk (1). Examination of milk-lipid concentration and composition is of interest because milk-lipid provides the major fraction of calories in human milk (1), contains fat-soluble vitamins (2), and provides essential fatty acids necessary for growth and development of the central nervous system (CNS) (3). Although milk-lipid concentrations show considerable variation both during a feeding and diurnally, the fatty acid pattern remains constant (4, 5) and, cross-culturally, milk fatty acids are more remarkable for their similarity than dissimilarity (3). However, the fatty acid composition of human milk responds rapidly and markedly to dietary changes (6, 7). [Reference]
Gee, thanks a lot!
But it seems that one thing there is general agreement about is that PUFA content of breast milk does vary a lot with diet, and it's DHA that varies the most. I looked at several studies that said more or less this and then found my way (through lists of "articles that cite this article," etc.) to a recent and large meta-study: "Docosahexaenoic and arachidonic acid concentrations in human breast milk worldwide." (Brenna et al., 2007) Here's the relevant bit from the conclusion:
Concentrations of DHA and AA in breast milk depend on the amount of these preformed FAs in the mother???s diet and their biosynthesis from precursors. Milk DHA content appears to be closely linked to maternal dietary DHA intake, with dosedependent linear increases in breast-milk concentrations of this nutrient with increased maternal intake (109). In our study, the 5 locales with the greatest breast-milk DHA concentration are Canadian Arctic, Japan, Dominican Republic, Philippines, and Congo (1.4???0.6%); all but Congo are coastal or island populations that have a high marine food intake. In contrast, the lowest breast-milk DHA values are for Pakistan, rural South Africa, Canada, the Netherlands, and France (0.06???0.14%). These populations are either inland or are developed countries, both of which are usually associated with low marine food consumption. Thus, the extreme values are consistent with studies suggesting that marine food???consuming populations have greater breastmilk DHA concentrations (7, 8).
The response of milk AA concentrations to maternal dietary AA intake is less predictable than that of DHA and may be more sensitive to the profile of other maternal dietaryFAs(30).
OK, so DHA is the yummy omega-3 that we want our babies to have a lot of, and the content of DHA in breast milk varies with the mother's diet. But what does this tell us about how much mothers should be consuming? Well for this I guess you'd have to look into infant brain development, which is a whole other tin of sardines. But we can get some insight into the topic indirectly by looking at what happens to the omega-3 content of the breast milk when we control for certain factors in the maternal diet. In this respect these two studies are very interesting:
Here's the core conclusion of the first paper:
After completing our comparative analysis of the fatty acid compositions of the milk lipids of the three major ethnic groups in Nigeria,3,8,9 we were struck by the wide range of the proportions of intermediate chain-length fatty acids found in the milk samples. The milk of some women contained as little as 10% de novo fatty acids in the triacylglycerol fraction, whereas, at the other extreme, C10-14 fatty acids accounted for nearly 70% of the fatty acids. This awareness moved us to ask: what untoward consequences might result when a woman produces a milk in which the fatty acids in the triacylglycerol fraction comprise mostly decanoic acid (10:0), lauric acid (12:0) and myristic acid (14:0)? Although these intermediate-chain fatty acids do offer metabolic advantages to the nursing infant, we reasoned that if their representation in milk fat becomes excessive (for example, >70%), they could supplant the more critical n-3 and n-6 fatty acids essential to the growth, development and general health of the exclusively breast-fed infant.
Therefore, we hypothesized that as the proportion of de novo fatty acids increased, it would be advantageous to the exclusively breast-fed infant if the essential fatty acids (linoleic and a-linolenic acids), and AA and DHA were preferentially incorporated into the triacylglycerol fraction of the milk. Without this kind of preferential selection of critical fatty acids during the assembly of the milk triacylglycerols in mammary tissue, the presence of large amounts of de novo fatty acids and a random incorporation of fatty acids into the milk triacylglycerols would reduce the quantity of PUFA in the milk. If this occurred, then as the contribution of de novo fatty approached 70%, the triacylglycerol fraction of the milk would become deficient in the nutritionally critical n-3 and n-6 fatty acids.
Our analysis of the fatty acid composition of milk fat indicates that, indeed, as the proportion of C10-14 fatty acids rises in human milk, there is preferential incorporation of the essential fatty acids, AA and DHA into the triacylglycerol component of the milk. This assertion is confirmed by our finding that as the proportion of C10-14 fatty acids increases from 15% to 65%, the proportions of stearic and oleic acid decline the most, by 69% and 86%, respectively (Table 1). In contrast, the proportions of linoleic acid, DHA, AA and a-linolenic acid, fell by only 44%, 39%, 28% and 2.3%, respectively.
Some brief explanation for the first paragraph. If I have understood correctly, the de novo fatty acids are the ones that are made in the breast. These are the medium-chain fatty acids, of length 10-14 carbons. Longer fatty acids (like the ones we read about all the time, palmitic (16:0), stearic (18:0), the monounsaturated oleic (18:1), etc. -- and also the PUFAs) are taken from the mother's pre-existing fat stores or from diet.
So the authors asked what happened when the proportion of the de novo fats increased to a very high amount. And lo and behold the proportion of the PUFAs decreased much less than the proportion of other fats. This would seem to imply that the mother's body is making an effort to keep certain minimum amounts of the PUFAs in the breast milk.
The second study, which refers to the first, shows something further: that when women are undernourished this "sparing" effect is even greater. (Actually it seemed that the second study in a sense disagreed with the first one, because they showed that the sparing effect is only significant when the women are undernourished. I was a bit confused about this to be honest.) Here's an excerpt:
Our primary finding emerged when we analyzed our data in such way as to permit us to examine the effect de novo fatty acid content has on the milk composition of Kanuri women. We were interested, in particular, in the effect that high levels of C10???C14 fatty acids had on the proportions of critical n-3 (a-linolenic acid and DHA) and n-6 fatty acids (linoleic acid and arachidonic acid). In a previous study of the milk lipids of Nigerian women, Schmeits et al. discovered that these four important n-3 and n-6 fatty acids, which are either essential or derived by elongation and desaturation of essential fatty acids, were preferentially retained in milk lipids at the expense of the non-essential fatty acids when the percentage of de novo fatty acids increased from 15% to 65%.9 We addressed this issue in the present study, using pooled data from all 89 of the Kanuri subjects, and found no such preferential retention of n-3 or n-6 fatty acids in the milk lipid fraction was observed (Table 4; Fig. 1). However, when we re-examined this question using fatty acid composition data for the least well-nourished Kanuri women, we discovered conservation of a-linolenic acid, DHA, and arachidonic acid when the de novo fatty acid proportion increased. Most remarkable was the effect that increasing proportions of C10???C14 fatty acids had on the percentage of a-linolenic acid in the milk lipids of the women with low BMI values; when the proportion of de novo fatty acids increased from 15% to 50%, the contribution or a-linolenic acid to the fatty acid total actually increased by 15%.
So that's another interesting result.
I've focused mostly on PUFAs. What about saturated fat, which you also asked about? Well, as you said there are fewer studies on this, probably because of the pre-existing bias of the system: saturated fat is evil, don't you know? But that may not be the only reason. I get the impression that there isn't as much need to be worried about saturated fat because there's pretty much always going to be plenty of it. There might be too little fat as a whole in the breast milk if the mother is undernourished, and there might be too much linoleic acid, but it's not as if the total PUFA content will get so high that there won't be enough saturated fat left over. That's just my impression.
(My brief mention of linoleic acid just now got me thinking. It occurs to me that if the mother's body has a system by which it preferentially spares the essential fatty acids and their metabolites, and if linoleic acid is one of those, then excess linoleic acid in the maternal diet could lead to an ironic backfiring of the system. The very system in place to conserve this essential fatty acid in case of scarcity will also conserve it in case of excess -- and lead to the "multi-generational obesity epidemic" that Stephan talks about in the post I linked to in my first answer. It's kind of a disturbing idea.)
Well, that's what I got. Here are a few other studies you might find interesting:
"Lipids of Bovine and Human Milks: A Comparison." (1990) Since you asked about cows versus humans; I wasn't able to look into this too much, but this could be a good starting point.
You should get a hold of this issue of the Journal of Pediatrics if you can: Volume 120, Issue 4, Part 2, Pages A1-S186 (April 1992). It's a special issue on "Lipids in Infant Nutrition." You can probably find more recent and more interesting stuff online, but it might be cool to have all that stuff in one place.
"Breast milk composition: fat content and fatty acid composition in vegetarians and non-vegetarians." (1985) No need to say why this one is interesting. But I'm sure it's flawed.
"The effect of a controlled manipulation of maternal dietary fat intake on medium and long chain fatty acids in human breast milk in Saskatoon, Canada." (2010) Just another one that looked kind of good. Recent as well.
"The lipids in human milk." (1996) A nice big summary by one of the biggest names studying the composition of human milk.
on September 17, 2010
at 05:37 AM
Probably a lot of factors. For one, there is probably a limit to how much the human mother can compensate. You can't give something you don't have in the first place. As it is, I have heard that females who have given birth have permanent damage like increased bone loss. Maybe that would not be the case if they had been eating paleo, but the point is, producing a child already does tend to put considerable strain on the mother. Many mothers get life threatening diabeties, hypertension, etc. THey are already pushed to the limit.
As for variability, there are a lot of genetic differences plus diets vary wildly. Cows have less variety in their diet than I would expect from the various diets of humans. And genetic difference may reflect optimum fat needs of the climate that the bloodline came from. Needs of children born in the tropics might be different from those born in the poles. SO that could account for some of the variation. If you were to check milk between different varieties of cow, some from Africa, and some from elsewhere, I would not be surprised if some variation was found.
on March 26, 2011
at 02:38 PM
Here's another post on breastmilk composition: http://180degreehealth.blogspot.com/2011/02/breast-milk-of-diabetic-mother.html