"Low testosterone levels are linked to a higher risk of heart disease, diabetes, and Alzheimer's disease."
While I wouldn't call 40% fat high (since the maximum upper limit of human protein intake is <40%, hence how wolves became domesticated and how lean meat "rabbit starvation" occurs¹,²). Really this study is based on a 40/30/30ish inverted zone diet.
Increased saturated fats (followed by mono), decreased polyunsaturated (Omega-6) fats (seed oils, especially oxidized fried foods), omnivorous diet, decreased carbs are all beneficial to male (and female) hormones (including insulin/glucagon and sex hormones) and thus weight and athletic performance.
Stuff like this really starts to delve into how multifactorial neuro-cardio-metabolic disease is, weighing the pros and cons of chasing one set of metrics at the expense of all others.
Medical Xpress: Low fat diets decrease testosterone levels in men.