Consulting nutritionist and clinical dietitian in India, Pooja Makhija, on fruitarian diet:

"All the pros that people claim about this diet is true — like weight loss, glowing skin, looking and feeling younger — however, it is short lived of two reasons. Firstly, it’s an unsustainable diet. The moment you get off the diet, you’ll put on the lost weight back again. Secondly, even if by a miracle, one follows it for years, initially the body can cope with the protein deprivation for two to three months but later due to protein deprivation it will result in hair loss, diarrhea, irritable gut, etc."

Statements like this should probably make me doubt my sanity and disbelief myself seeing and feeling my long hair after ~ 20 years of such protein deprivation. I do not have any of the listed symptoms. But I do eat seeds often, and the statements of the nutritionist was probably issued without proper understanding what fruitarian diet is - generally speaking, on fruitarian diet 3/4 or more of the calories, 75%, should be derived from fresh fruit in botanical sense, and supplemented with other, mainly plant foods, derived with minimal destruction of other living organisms.

Nevertheless, "deprivation" is a too strong of a word, considering that even just juicy sweet culinary fruit contain protein.

But what statements like this can certainly cause, is polarisation in public opinions on healthy diets, and distrust towards medical and official representatives by certain groups of people. 

This dietitian did not offer any case studies, or any scientific data to support her statement, and she used definitive language, mixed with exaggerations. She basically claims without any doubt that

1. a diet based on fruit is unsustainable and only "by a miracle" can be followed for a couple of months,
2. and that after a three months the inevitable severe loss of health kicks in.

Both statements can be proven false with just one case study, or better, a few. I sustained myself on juicy fresh fruit only (sweet and unsweet) for many month a year, many times, and reading such supposedly educated opinions is sad and funny to me. This lady does not know. The modern nutritional science does not know for sure. And, considering everything we do know, it is possible to stay healthy eating primarily fruit for long periods of time. 

If she would say:

1. a diet based on sweet juicy fruit only is likely unsustainable for most people,
2. in a longer than a few month run there might be a problem with consumption of lower than currently recommended levels of protein with possible severe health consequences,

I would agree, and it would be a reasonable recommendation not to follow the diet. 

By the way, one in five US adults has signs and symptoms of irritable bowel syndrome, and I could find no information on its causation by or correlation with protein deficiency.

Dhvani Shah, Healing Diet Specialist, says that a Fruitarian diet will be beneficial if had just for one day as it helps in "detoxification":

"If the diet is continued for more than a day, it will lead to stubborn fats that don’t burn and the lack of carbohydrates and proteins will lead to health issues. Those who are part of a weight loss crash course, they can opt for the Fruitarian diet as a plateau breaker. Incorporate as many varieties of fruits. But it is essential to stick to the diet only for one day."

There is little evidence that detoxification diets eliminate toxins from your body. Untrustworthy people sell "detox" diets and products and claim miraculous effects. Usage of this term by a diet specialist, presented as an authority in the field, is questionable. Many individuals who try various diets call all of their negative experiences with them "detoxing." I did not experience any noticeable detoxification myself, and I was very surprised when I learned that people saw their temporary skin problems and other bad experiences on a new diet as a positive outcome. 

This "healing specialist" talks about "lack of carbohydrates" in fruit? Maybe, certain complex carbohydrates, but none of those, as far as I know, belongs to the essential nutrients category, and all of them our body will split down to simple sugars. Maybe, not eating enough sugars? That can be a problem, but diet advisers need to communicate their recommendations clearly if they want them to be followed. 

It is so difficult to find a credible health advice. I wish some responsible publicly-funded agencies would invest more resources in popularizing the results of modern research and general knowledge in nutrition.