If it’s your main source of protein.
A 200Lb adult needs a minimum of 140g of protein daily to remain healthy.
A single serving of peanut butter has 190 Calories, and only 7g of protein.
If that 200Lb adult was getting just half of their protein from peanut butter, they would be consuming 1,900 calories in the process. Even if they are active enough to justify that caloric intake, they would still be consuming 160g of fat, which is double the daily recommended amount. It’s the nutritional equivalent of drinking a 2/3 cup portion of cooking oil every day.
Tl;Dr: Do not make peanut butter your main source of protein.
A 200Lb adult needs a minimum of 140g of protein daily to remain healthy.
The standard recommendation is about 0.8g per kilogram of body weight. So 200 lbs is 91 kg, which corresponds with 73g.
There’s some more recent advocacy for more protein, especially for active or older people, but that’s talking about more than just the minimum requirements to be healthy, and more towards optimizing for performance.
With their high protein concentration, peanuts are used to help fight malnutrition. Plumpy Nut, MANA Nutrition,[67] and Medika Mamba[68] are high-protein, high-energy, and high-nutrient peanut-based pastes developed to be used as a therapeutic food to aid in famine relief. The World Health Organization, UNICEF, Project Peanut Butter, and Doctors Without Borders have used these products to help save malnourished children in developing countries.