Mark may be getting lower amounts of nutrients and vitamins, namely omega-3s and omega-6s. This would directly affect the brain and normal body functions because the body needs vitamins/nutrients to thrive. This could affect the chemical balance in his brain, resulting in depression/schizophrenia/other issues, including eating disorders. Cutting down on fats might also result in overeating carbs and protein, which leads to an overbalance of nutrients -- and a host of other health issues.Not getting enough fat could also affect bone growth.
Hope this helps:D
Have a great rest of a brainly day!