Anecdotal Evidence
Logical fallacyTreating a personal story or an isolated case as though it outweighed systematic evidence. Individual cases are real, but they do not establish general patterns.
An everyday example
“My grandfather smoked until he was ninety, so smoking can't be that harmful.”
The same move in this debate
“I know someone who tried veganism and felt awful, so it doesn't work.”
Where this appears
A single personal experience is offered to settle a question that population-level evidence addresses directly. The experience is good evidence about that attempt and weak evidence about the diet in general.
The speaker moves from his own experience of gaining bulk when eating more meat to a general claim that humans need animal products to survive. That single case cannot outweigh population studies and the position of dietetic bodies. It also does not separate the effect of meat from the effect of simply eating more protein.
It cites case reports of poisoning from extreme intakes, raw beans or existing kidney disease, then presents them as harm at 'typical dietary doses'. The cases do not show that, and they say nothing about the risk of an ordinary plant-based diet.
The speaker sets client outcomes seen in their own practice against the population studies and treats those outcomes as the better evidence. These are uncontrolled, short-term and self-selected cases, and they cannot outweigh decades-long cohorts and controlled comparisons.
The speaker set aside population studies because they did not match what he sees in his own clients, treating uncontrolled personal observation as outweighing systematic long-term evidence.
A single case is offered against a general claim that would require population-level data to assess. The case is real and is doing more work than it can carry.