I’m afraid to say…
… it is TRUE!
If dietary fat gets too low, it seems that testosterone levels do decrease significantly
So what is too low?
In one study a reduction in testosterone was seen when dietary fat was less than 20% of the total daily calories.
Another study, reported that men who deliberately restricted their dietary fat intake had a significant reduction in serum testosterone of about 7.5%
Furthermore, low fat intake (<20% of calories) has been shown to result in reduced endurance performance.
If training performance suffers and your testosterone levels are low then, you REALLY ARE GOING TO STRUGGLE to see the changes you want!
When setting protein and carbs for optimal performance, lean muscle gain, and fat loss most experts agree on the ideal intakes.
Or they at least are very close to each other in their guidelines.
Fat intake is a different story!
There is not a consensus on the amount of fat healthy individuals should eat.
Some people provide grams per day targets. Some identify a percentage of your overall intake.
Personally, I think a grams per KG approach is best. This make your fat intake relative to your size. This make it mote specific to you and your needs.
I suggest having between 0.6-1 gram of fat per KG of body weight. Anything up to 1.25g/kg seems effective.
This is enough to support optimal hormonal function
When in a surplus you could actually choose the lower end of this range as hormonal disruption is much less likely. In that case, I’d suggest bumping your carbs up to replace the calories.
In a fat loss phase, I’d shoot for the higher end of the range as hormonal function is more likely to be negatively affected in a deficit.
Adherence to the plan is the key to the success with and diet As such, allowing personal preference in a range of 0.6 to 1.25 grams of dietary fat/kg seems a good range to aim for.
TLDR; Don’t let your fat intake drop too low. If you do your testosterone might crash. If that happens then, your ability to build muscle, lose fat, increase strength, and recover from training, will all be sub-optimal.