According to Health.com, side effects of a low-carb diet may include sadness, stress and can lead to belly bloat and constipation. A diet which prohibits carbs may offer adverse results in the long-term, holding onto fat-cells instead of getting rid of them.
In a study of people who ate carbs versus those who did not, the carb eaters were happier, calmer and were able to focus better. The test subjects who were carb-deprived felt stressed because carbs boost certain chemicals in the brain that regulate mood and stress. A diet high in protein and fat may interfere with these chemicals. Diet specialists also agree that cravings increase if carbs are cut out of a diet entirely. The stress of cutting carbs causes levels of the stress hormone cortisol to rise, increasing appetite and causing weight gain. Constipation is a side effect of a low-carb diet, with 68 percent of participants in one study affected.