Ugolev studied digestion under the guidance of the best physiologists in the country. At the age of 24 he defended his Ph.D. thesis and at the age of 32 his doctorate. In the same year Alexander Mikhailovich discovered membrane digestion. This work was three times nominated for the Nobel Prize and forced to revise the classic scheme of the evolution of the digestive process. Ugolev proved the universality of the process from protozoa to humans.

In 1960 the scientist began working at the Institute of Physiology named after I.P. Pavlov of the USSR Academy of Sciences in the laboratory of general physiology of reception under the leadership of Academician Vladimir Nikolaevich Chernigovsky.

In 1964, at the age of 37, Ugolev became the head of the laboratory of nutritional physiology. The main scientific directions are the study of the physiology of membrane digestion and the non-digestive effects of the intestinal hormonal system.

Since the late 1960s Aleksandr Mikhailovich was a leading consultant on nutritional problems for astronauts at the Institute of Biomedical Problems of the USSR Ministry of Health. From a physiological point of view, he analyzed the problem of using artificial food for astronauts in extreme conditions. In addition, the scientist participated in the selection of monkeys for space flight.

At the age of 40, Ugolev became the youngest corresponding member of the USSR Academy of Sciences, 18 years later — an academician.

With the participation of Alexander Mikhailovich, the science of gastroenterology arose on the basis of the doctrine of the physiology of nutrition. He formulated the theory of balanced nutrition and developed diets for long-term space flights.