An animal study comparing five diets shows that one diet really doesn't fit everyone, and what works for some may not be best for others.
There were four groups of genetically (almost-)identical animals, with genetic differences between any two of the groups translating to roughly the same as those of two unrelated people. The test diets included: an American-style diet (higher in fat and refined carbs, especially corn); Mediterranean (with wheat and red wine extract); Japanese (with rice and green tea extract); and ketogenic, or Atkins-like (high in fat and protein with very few carbs). The fifth diet was the control group.
One of the four genetic types did very poorly when eating the Japanese-like diet, developing signs of liver damage. Two types did well on the Atkins-like diet, but two did very badly (one became very obese, while the other became 'skinny-fat' — apparently a healthy weight but with a high percentage of body fat.
Two types became very obese, with signs of metabolic syndrome, on the American-style diet, while the other two were less negatively affected. With the Mediterranean diet, some groups were healthy, while others experienced some weight gain.
(2018). Improving Metabolic Health Through Precision Dietetics in Mice.
Genetics. 208(1), 399 - 417.