Buddha’s advice for monks to beg for food and to accept it all is poisoning many monks because Buddha either didn’t know or didn’t care that food could heal or poison (actually, I do not really think this practice really originated from the Buddha’s advice -see note one, below.)
Eating alms food in imitation of Shakyamuni Buddha’s lifestyle means that nearly half of Thailand’s monks are obese and suffering related health problems such as high blood pressure, diabetes and high cholesterol.
|Dr. Chotechuang (MD)|
According to a new study  by Dr. Chotechuang (MD) Buddhist monks are literally being poisoned by the bad advice handed down from Buddha. Alms from the well-meaning faithful often consist of drink juices, sweet tea, snacks and street foods all of which are laden with fat and sugar which not only lacks the essential nutrition needed to live a healthy and happy life but can actually act as a poison. In addition, the largely sedentary nature of temple monastic life is adding to the problem.
Realizing that Buddha’s advice on eating is literally poisoning monks a new initiative has been launched to promote healthy living and enable the monks to prepare nutritional meals and reject the unhealthy food . This is will help the monk live longer healthier lives and also reduce the cost of medical fees that are currently paid for by the Thai government.
This issue is wider than Thailand and 80% of Buddhist monks from Sri-Lanka die of heart disease which is thought to be largely down to diet  prompting calls for monks to break with tradition and watch their diet [4.]
In fact, Shakyamuni Buddha himself died of food poisoning because the food donated had not been cooked properly, but it seems no-one around learned any lessons from that [2.]
Actually, it was not Shakyamuni Buddha who started the tradition of yogins begging for food and this was the standard practice for seekers in Ancient India. This practice clearly continued in Buddhism and got codified in the sayings attributed to the Buddha and written down hundreds of years after his death, in a language he didn’t speak and in a country he didn’t live it. In other words, this tradition did not actually start with the advice of the Buddha but was part of the socio-cultural-religious practices of the time and place that Buddhism took root. Or in other words, it is the Buddhist tradition rather than the Buddha himself which passed down this practice that is questionable.
 http://www.bangkokpost.com/archive/almost-half-monkhood-overweight/897276 Accessed 6/5/17
 In the traditional account of the Buddha’s death he was poisoned by eating a piece of rotten pork. (cf, Mahaaparinibbaana-sutta.)
 Dr. Gunasena, (11th October 2012), The Island, “Poor Health of Monks”.
 http://www.bbc.com/news/av/health-21296153/sri-lankan-monks-told-to-watch-diet Accessed 6/5/17