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I don't think this is a good representation of the "latest" in nutrition.
Meta-analysis indicates that replacing saturated fat with unsaturated or even carbs results in weight loss.
Protein restriction does not "rev up the metabolism" and is bad for maintaining lean mass.
How much protein do you need?
Isoleucine and valine are specifically the Amino Acids that are problematic, but really to avoid them you need to avoid protein.
The difficulty with meta-studies on saturated fat vs unsaturated fat is that studies use lard or chicken fat as their example of saturated fat, when in reality those two fats are highly unsaturated. This leads to farces like "Learning and Memory Impairment in Rats Fed a High Saturated Fat Diet" They analyze the fatty acid composition of their lard and it is only 30% saturated. Despite this, the study uses lard as their Saturated fat intervention.
Specific to Hooper et al. (2020) that your linked article uses for it's argument, I am looking at their studies and am having trouble finding which showed a benefit from substituting polyunsaturated fat with saturated fats. At the most, I see some that show benefits from reducing fat entirely, which I would agree with. Reducing all fat will reduce the amount of total linoleic acid and a High Carb, low fat diet would be good from my understanding. (Low fat means < 15% calories from fat, most low fat studies have 30% of calories from fat, which is practically the normal amount of fat intake in a SAD, but that's another story.)
Hooper's results don't seem really indicative of anything. Your link extols the results of this figure, but outside the couple tails where they got the Saturated fat intake really low, there doesn't seem to be a clear correlation between increasing Sat Fat and disease. Under 9% of Sat fat only has data on a few risk events, which makes me think that there are only a handful of studies with that amount of sat fat. I'm trying to figure out if this data point reflects the studies that went with High carb, low fat.
However, the figure in question still shows that when dietary saturated fat reaches >12% of calories, markers improve! Risk of Stroke goes way down. CVD goes down.
Weight isn't studied in the Meta-analysis at all.
You can hardly hold this random rat study against me.
I encourage you to check the studies in the meta and see that this is not going on.
Review says:
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Table 4 additionally shows that reducing total fat has no impact on cardiovascular events.
It would be a big surprise indeed if a moderate amount of saturated fat is bad, but a small or large amount is good. The relationship is most likely to be linear.
It was, of course.
This appears to be a study on untrained men? I agree that if you're okay with the average untrained physique, 44g is enough (and also not that far from the recommendation of 54g for a 150lb person).
Most of these are mouse studies, so let's look at the first one.
The restricted protein group in this study was eating protein at the RDA of 0.8 g/kg, which again is fine for people without aspirations to build muscle (which doesn't apply to OP).
The study doesn't seem to report if the change in weight loss between PR and CR is significant or not. However, looking at figure 1, id suspect not, especially when removing the 300 pound guy in the PR group.
As far as metabolism goes, figure 2 shows that the CR had a much lower metabolic rate at baseline vs the PR group, so the randomization seems to have failed. The PR group's variance is way bigger too, perhaps due to the aforementioned outliers.
Here's a more sophisticated metabolic ward study with three isocaloric overfeeding diets with varying protein content. They're using dexa scans, CO2 respiration rate, and doubly labeled water to measure body comp, resting energy expenditure and total energy expenditure, which are gold standard methods.
https://jamanetwork.com/journals/jama/fullarticle/1103993
Overall, higher protein intake is more favorable for body composition (holding calories equal), and increased metabolism more than lower protein intake.
Are we looking at the same Hooper study? It's funny how we can both look at it and zoom on different things:
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I looked through a few of the studies they reviewed but most don't really demonstrate a low PUFA/high Sat Fat diet anywhere.
The Black Study reduced fat entirely (not substituting PUFA for Sat fat) and found that keeping fat under 20% of calories helped reduce skin cancer.
The DART Study advised men to increase ratio of PUFA to SFA, but: "The advice on fat was not associated with any difference in mortality." Men who were advised to eat fatty fish did better, but I'm open to the idea that it's the O3:O6 ratio that matters, meaning increasing O3 might be beneficial to people (especially in the context of a high O6 diet).
Then we get to the Houtsmuller study, which look like it's going to actually address the PUFA thesis. Two groups of people fed a controlled diet, one diet has 4x as much Linoleic acid as the other. Sounds good. He doesn't give a lot of details about what is in each diets how he assessed the Linoleic acid quantity in the study. But let's take him for his word. There are a couple details that stand out to me:
First is, "The linolcic acid content of diet II was 4 times that of diet I, being 20.4 gr/1000 kcal for group II and 5.3 gr/1000 Kcal for group I."
According to the PUFA hypothesis, it's more like a cliff than a gradient. Humans naturally eat around 4-5 gr a day of PUFA without seed-oil or mono-gastric animal sources. This study has the Sat Fat group get twice that.
The other detail is they mention one of the sources of Sat Fat, "except for 4 patients of group I who preferred butter over saturated margarines." The Sat Fat group's intervention included getting fed partially-hydrogenated margarine. Which means lots of transfats. The negative effect this study found can possibly be explained by the amount of transfats in the Sat Fat arm of the study.
I'll admit I didn't check every study, but the ones I checked aren't really applicable to anything I'm concerned about. The only one I saw that clearly substituted Linoleic Acid for actual Sat Fat was the Sydney Study, which showed that substituting Margarine for Butter actually increased risk of Cardiovascular disease.
That said, the Sydney study Margarine probably had transfats. I'm not going to state that the Sydney study proves Sat Fat is the best, but it does support my primary point, which is that nutritional studies on fats are Terrible, do not account for common confounders, and a meta-analysis of a bunch of terrible studies does not make for good data.
I'm talking about OP's wife. OP seems to want his wife to become slimmer, not a body builder. I'm indicating that to lose weight might require cutting protein down to the bare minimum (around 50g), something that is left out of a lot of advice. Losing lean mass when losing weight can actually be quite good, as you don't want a lot of extra skin hanging around.
Yeah, the meta shows no effect on all cause mortality - but that's not the question we're discussing. I only brought it up since you responded to the graph of mortality outcomes rather than weight outcomes.
In fact, the meta shows that substituting unsaturated for saturated fats reduces weight and there's no association If the studies were actually controlled metabolic ward studies, they'd probably show no effect with isocaloric diets.
This seems like an extremely specific and unusual claim, perhaps a result of undeniable studies chipping away at the upper limits of what people can defend. We definitely shouldn't privilege weird rat studies over human ones to defend this claim. Linear relationships should be the default assumption.
The lean mass lost is not skin, it's internal organs, muscle mass, water weight, etc. The amount of skin remaining after weight loss does not depend on the diet.
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