Acides gras, évolution et santé

Comparative analyses of chromatin landscape in white adipose tissue suggest humans may have less beigeing potential than other primates
Smain-Lenz et al.
Genome biology and evolution, 2019
https://www.biorxiv.org/content/biorxiv/early/2019/01/18/524868.full.pdf

Taken together, these results suggest that humans shut down regions of the genome to accommodate a high fat diet while chimpanzees open regions of the genome to accommodate a high sugar diet.

https://nutrirejournal.biomedcentral.com/articles/10.1186/s41110-018-0078-x

In addition to the energetic benefits associated with greater meat consumption, it appears that such a dietary shift would have also provided increased levels of key fatty acids necessary for supporting the rapid hominid brain evolution [60].

Half of human brain composition is fat, and 20% of its dry weight is long-chain polyunsaturated fatty acids (LCPUFAs). Consequently, improvements in consumption of dietary fat were a necessary condition for promoting encephalization [61, 62].

Mammalian brain growth is dependent upon sufficient amounts of two LCPUFAs: docosahexaenoic acid (DHA) and arachidonic acid (AA), and it appears that mammals have a limited capacity to synthesize these fatty acids from dietary precursors. Hence, species with higher levels of encephalization would have greater requirements for DHA and AA [62]. Consequently, dietary sources of DHA and AA were likely limiting nutrients that constrained the evolution of larger brain size in many mammalian lineages [63].

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Past and Present Insights on Alpha-linolenic Acid and the Omega-3 Fatty Acid Family
Aliza H. Stark et al., 2015
https://www.tandfonline.com/doi/abs/10.1080/10408398.2013.828678?casa_token=YehE6gKCJ4gAAAAA:rofWbXRDuZfsD-b37XhVeRBW_LddGQXNJrQXm_pWUpghtILZ77hreoGWgIRSsCMs98jczMcJTR2M

Alpha-linolenic acid (ALA) is the parent essential fatty acid of the omega-3 family. This family includes docosahexaenoic acid (DHA), which has been conserved in neural signaling systems in the cephalopods, fish, amphibian, reptiles, birds, mammals, primates, and humans. This extreme conservation, in spite of wide genomic changes of over 500 million years, testifies to the uniqueness of this molecule in the brain and affirms the importance of omega-3 fatty acids.[…]
Unlike humans, rats and mice can readily convert ALA to EPA and DHA

Zebra was preferred over impala, because of the nature and abundance of its fat. The Hadza, like many other traditional hunters, value fat more highly than protein
(Woodburn pers. comm.; Speth 1983). They classify fat as either ‘hard’ (e.g. bovids) or ‘soft’ (e.g. equids). Soft fat is particularly valuable because it can be fed to babies within their first few weeks of life. Adult male zebra are highly regarded because they can provide relatively large quantities of soft fat. […] they regard horseflesh as the best food source. Because of the high calorific value of horse fat, when the weather is very cold and, in particular, when it is necessary to travel long distances […] Horse flesh can, in fact, be very greasy; however, the quality of the grease,
or fat, is very different from that of sheep or cow and is, indeed, far more digestible. My steppe and forest-steppe informants consider horse fat to be very good for human health and superior to that of sheep or cattle. […] The most valued parts of the carcass -that is, those with the highest fat content – are offered to guests. This includes the cranium, with the brains, eyes and ears, which are given, in particular, to old people. The meat and fat on the back of the neck under the mane and on the ribs are particular delicacies, offered to honoured guests. […]
three different types of fat used for weaning babies:
– Camel’s hump (southern Kazakhstan)
– Ram’s tail boiled in milk (ubiquitous)
– The fat from over the horse’s sternum and under its mane (ubiquitous)
[…] fermented horse milk, or kumys, ‘plays an extremely important role in Kazakh everyday life. […] Because it is regarded as the best substitute for human milk, unfermented mare’s milk is fed to human babies ; like horse fat, it is an important weaning food.

Acides gras et fonctions cognitives

Association between maternal intake of n-6 to n-3 fatty acid ratio during pregnancy and infant neurodevelopment at 6 months of age: results of the MOCEH cohort study.
Kim H et al.
Nutrition journal, 2017
https://www.ncbi.nlm.nih.gov/pubmed/28420388

Cognitive and motor development of infants at 6 months of age was assessed by the Korean Bayley scales of infant development edition II (BSID-II) including the mental developmental index (MDI) and the psychomotor developmental index (PDI).

RESULTS:

Maternal intakes of n-6/n-3 PUFAs and linoleic acid (LA)-to-α-linolenic acid (ALA) ratio (LA/ALA) were 9.7 ± 6.3 and 11.12 ± 6.9, respectively. Multiple regression analysis, after adjusting for covariates, showed that n-6/n-3 PUFAs was negatively associated with both the MDI (β = -0.1674, P = 0.0291) and PDI (β = -0.1947, P = 0.0380) at 6 months of age. These inverse associations were also observed between LA/ALA and both the MDI and PDI (MDI; β = -0.1567; P = 0.0310, PDI; β = -0.1855; P = 0.0367). Multiple logistic regression analysis, with the covariates, showed that infants whose mother’s LA/ALA were ranked in the 2^nd, 3^rd, and 4^th quartile were at approximately twice the risk with more than twice the risk of delayed performance on the PDI compared to the lowest quartile (1^st vs. 2^nd; OR = 2.965; 95% CI = 1.376 - 6.390, 1^st vs. 3^rd; OR = 3.047; 95% CI = 1.374 - 6.756 and 1^st vs. 4^th; OR = 2.551; 95% CI = 1.160 - 5.607).

CONCLUSIONS:

Both the maternal dietary n-6/n-3 PUFAs and LA/ALA intake were significantly associated with the mental and psychomotor development of infants at 6 months of age. Thus, maintaining low n-6/n-3 PUFAs and LA/ALA is encouraged for women during pregnancy.

When a wide range diets are evaluated in animal systems, it is possible to see that the level of DHA found in the blood of animals fed diets containing only LA and ALA can reach levels similar to that of animals fed diets rich in fish oil, but only when the

ALA:LA ratio is high and the total amount of dietary polyunsaturated fatty acids (PUFA) is low. Diets that are rich in either monounsaturates or saturates meet these requirements. Importantly, there are human infant studies that have tested such diets and demonstrated that human infants accumulate greater amounts of DHA than when diets are high in LA. It might be time to reconsider the dietary requirement of the two essential fatty acids LA and ALA in human infants

in terms of their ability to enhance endoge nous synthesis of DHA rather than more

adult biomarkers like cholesterol levels.

The dietary n6:n3 fatty acid ratio during pregnancy is inversely associated with child neurodevelopment in the EDEN mother-child cohort.
Bernard JY et al.
The journal of nutrition, 2013
https://www.ncbi.nlm.nih.gov/pubmed/23902952

This suggests that the ratio between maternal dietary n6 and n3 (LC)PUFA intake possibly influences the child’s brain development during fetal life but not during or by breastfeeding. However, breastfeeding might compensate for prenatal imbalance in maternal dietary n6:n3 fatty acid ratio.

Current evidence suggests that consumption of LC omega-3 PUFA, particularly DHA, may enhance cognitive performance relating to learning, cognitive development, memory and speed of performing cognitive tasks. Those who habitually consume diets low in DHA, children with low literacy ability and malnourished and older adults with age-related cognitive decline and mild cognitive impairment seem to benefit most. However, study design limitations in many RCTs hamper firm conclusions. The measurement of a uniform biomarker, e.g., % DHA in red blood cells, is essential to establish baseline DHA-status, to determine targets for cognitive performance and to facilitate dosage recommendations. It is recommended that future studies be at least 16 weeks in duration, account for potential interaction effects of gender, age and apolipoprotein E genotype, include vegan/vegetarian populations, include measures of speed of cognitive performance and include brain imaging technologies as supportive information on working mechanisms of LC omega-3 PUFA.

Acides gras saturés

Dietary stearic acid regulates mitochondria in vivo in humans
Deniz Senyilmaz,
Nature communication, 2018
https://www.nature.com/articles/s41467-018-05614-6

This could explain part of the epidemiological differences between C16:0 and C18:0, whereby C16:0 increases cardiovascular and cancer risk whereas C18:0 decreases both.

Diet-Heart Hypothesis

Several articles have concluded that associations between high cholesterol and premature death are lacking and advocate revision of current guidance advising low consumption (<10%) of saturated fat.123 Ramsden and colleagues recovered 45 year old data from the Minnesota Coronary Experiment, a randomised controlled trial conducted in state psychiatric hospitals and nursing homes in Minnesota, USA, and reassessed the effect of a diet rich in linoleic acid on serum cholesterol and mortality.3 The authors found that the diet lowered total cholesterol but did not reduce the risk of premature mortality and might even have increased it.