A general guideline we like to use as a starting point is based on the amount of estimated lean body mass (LBM) a person has. Since “lean tissue” is composed of everything other than fat tissue, it also accounts for your organs (like your brain) that require fatty acids in order to function optimally.
LBM = Body weight x (1 – Estimated body fat % as a decimal)
Ex: 200 pound person with 10% body fat
180 = 200 x (1 – 0.1)
The calculation for minimum fat intake we use is:
Males = .3g/pound of LBM , .66g/kg of LBM
Females = .4g/pound of LBM, .88g/kg of LBM
Females tend to have a slightly higher demand for fatty acids due to their difference in hormonal profile and cycles.
Using our example from above, the person with 180 LBM would have a minimum fat intake of:
0.3 x 180 = 54g
Again, this is a guideline for when calories are getting low. If someone is in a surplus for hypertrophy, they likely don’t have a reason to get close to these levels.
In some extreme cases (end of a photoshoot or contest prep for example) we might dip below these levels slightly for a very short time. Perhaps 1-2 weeks. That short of a duration is unlikely to have any adverse side effects.
Also keep in mind that this is in context of a weekly average. For example, you could have lower fats on training days that are at or slightly below the minimum, but on non-training days you have more fats in the diet so that over the course of the week you are above the minimum.