Whilst most of us worry about getting enough protein or calcium the reality is the biggest deficiency in our diets is fibre. 97% do not get enough fibre. Fibre only exists in plant based foods, vegetables, grain, fruit, beans etc so with our western diet revolving around animal based products is causing us to face an uphill battle. It is recommended that we get at least 30g per day, but most of us get around half of that. https://www.bbcgoodfood.com/howto/guide/spotlight-high-fibre-diets
This leads to worrying health risks including diabetes, irritable bowel syndrome, constipation, diverticular disease, colon cancer and heart disease. Also a little know fact is that a fibre rich diet can aid weight loss http://www.eatingwell.com/article/15696/is-fiber-good-for-weight-loss . I can vouch for that, since converting to a plant based diet I am never hungry.