I have in my fridge a delicious-looking bowl full of fat rendered from making stock with a kilo of very fatty beef ribs. Trouble is... it's not grass-fed beef.
After making the stock, I ate the strips of meat on the ribs, and nibbled on some of the abundant fat on them, but resisted the urge to eat all of it, as I wasn't convinced it was a good idea nutritionally speaking. But I kept the rendered fat from the stock, just in case...
So my question is this: should I use this fat? Will it do more harm than good or vice-versa?
The two main things I'm concerned about, given the non-grassfed (and non-organic) origin of the meat, are: 1) presence of high concentrations of toxins in the fat; 2) high omega-6/omega-3 ratio (i.e. pro-inflammatory).
On the subject of the toxins from antibiotics, hormones etc, unfortunately I think the answer is that we don't know, due to simple lack of evidence on the matter. By definition, the people who decide safe levels think the levels in food are safe, but their general outlooks seems to be that they don't know for sure, but there's no evidence of any danger. Fwiw, I eat tonnes of conventional meat and am sure it's beneficial compared to less conventional meat.
[Edit: This website- credit to Acton- suggests that contaminants in meat aren't a concern.]
The omega 6:3 thing is a worry. My solution is to not worry in general about the omega 6 in meat, but avoid what fat I can by trimming and pouring off excess. At first when I went high-fat paleo I thought "right, I ought to get start eating the fattiest cuts I can find!" but then soon realised that butter was likely far more nutritious (A, K2, butyrate) than animal fat and far less omega 6. I've heard the claim that properly raised animal fat should contain a wealth of nutrients, including goodly sums of vitamin D, but on paper (i.e. www.nutritondata.com it doesn't come across. Grass raised fat works out about the same as butter, just more MUFA less SFA (up to debate if that's good/bad/neutral). Stephan has a ncie group of charts comparing fats here.
For all that, I'd be tempted to use the tasty animal fat anyway, at least beef's the least omega-6y conventional animal meat!
Second edit! This new piece has some nice graphs showing the differences between conventional and grassfed animals.
I don't know about the toxins. Omega-6 is strongly implicated by many as disease promoting. Ideally you really don't want to be eating any omega-6 at home besides what comes from naturally raised animal. You will get plenty of omega-6 from eating outside of home. The other concern here is that the fat comes from rendering stock, which could mean you have already applied a lot of heat to your fat, which could make the omegas go rancid. Normally you want to eat your ribs (including the fat) and then make stock with (just) the left over bones, which should yield only a small amount of fat.
We all have to compromise on our nutrition, so it is up to you and your budget if you want to compromise on this. If you do, I would supplement with omega-3 (fish oil) so you aren't omega imbalanced.
There are some misconceptions about grass-fed meat floating around these days.
First, grass fed meat does have a better n-3/n-6 balance, but it has, in absolute terms, more omega 6 than does grain fed meat. Of course, it also has more omega 3s and more PUFA overall. However, for those that try to restrict all PUFAs (and achieve balance) and have unlimited SFAs, it is as good (or better) to buy grain fed meat and take a fish oil pill on the side.
Second, grass fed meat has 3-5X as much ruminant trans fat as grain fed meat. CLA and vaccenic acid may be good for you, but likely only up to a point. Recent studies have shown that after a point such trans fats are as bad as industrial trans fats. Since I like to eat a very high fat diet (and ruminant fat is a convenient source of low PUFA fat), I have to be careful about having to much ruminant trans fat.
Lastly, I pretty sure it is a myth that grass fed meat is safer from an e coli perspective than organic grain fed meat.
Thus, organic grain fed meat (which tastes better -- superior marbling) might be better for some people.
Regarding O6 -- I don't think we can say that grass-fed has more. Per http://www.nutritionj.com/content/pdf/1475-2891-9-10.pdf:
"Table 2 shows no significant change to the overall concentration of n-6 FAs between feeding regimens, although grassfed beef consistently shows a higher concentrations of n-3 FAs as compared to grain-fed contemporaries, creating a more favorable n-6:n-3 ratio."