THE PHYSIOLOGY OF FOOD

Otago Witness, Issue 3197, 23 June 1915, Page 32

THE PHYSIOLOGY OF FOOD

LECTURE BY PROFESSOR

MALCOLM

The fifth of the series of popular lectures being delivered at the University this winter was given in the Chemistry Lecture Room on the 16th by Professor Malcolm. Mr J. H. Walker presided, and there was a large attendance, including a considerable number of lady students. Dr Malcolm’s subject was “The Physiology of Food,” and his lecture was made peculiarly practical and interesting means of elaborate and careai y PJ e P c ’ " series of exhibits, and by the use ot tables and charts. In opening, he explained that strictly the title of the subject should haae been “diet” or “dietetic*.” He drew attention to the great variety of foodatuns ; used by the human race, and stated tuat the main constituents of all these were protein, carbohydrates, and tat. Discussing protein first of all, be illustrated it* characteristics from the case of white ot egg. Nitrogen was an important elemen in protein, which was the only foodstuf that .contained nitrogen. Protem was therefore more essential in a, diet than were carbohydrates or fat. Carbohydrates contained a great many substances obtained from the vegetable world, notably the starches and sugars. The great avidity of glucose for oxygen rendered it ot great value in the body. That was why sveee a substances were so effective in sustaining energy in the body. Fat differed from carbohydrates in being less readily oxydised, but when it was oxydised it yielded far more heat than carbohydrates. He explained that the reason for the constant taking in and rejection of food by the body was that energy was developed in the process. He referred particularly to “potential” energy, such as that possessed bv water at a height or by many chemical substances. Foodstuffs had the power of uniting with oxygen, and in doing this energy was produced somewhat in the same way as it was produced by falling water. All forms of energy were convertible one into another, and in all these transformations a certain amount of heat was generated. AH forms of energy tended to degenerate into heat, and heat was taken as the standard or measure of -energy. He explained that the calory or" unit” of heat was the amount of heat that would raise the temperature of one kilogram of water to one degree centigrade. The caloric value of protein and of carbohydrates was practically the same, 4000 or 4100 - r but,fat had a much higher potential energy than either of these, and its caloric value was 9030. Speaking of the body purely as a machine, he said it converted food into heat and muscular energy. The body differed from all other machines in that it made use of all the heat generated. Another remarkable characteristic of the body was its extraordinary powers of self-repair. The two great purposes of a diet were to supply sufficient energy to run the machine and sufficient material for purposes of repair. He described the large amount of energy required by the lungs, by the heart, and* in numerous' other delicate unconscious processes of the body. All muscular movements involved a very considerable amount of muscular energy —much more than would at first appear." The amount of internal work was largely increased by any external work. People doing strenuous muscular work required double the number of calories that would be required by a person lying in bed. He quoted numerous interesting calculations, such as that an hour’s walk caused an additional expenditure of 260 calories, or one ounce of fat Cold had a great influence on the amount of foodstuffs required. A person of small size required more food in proportion, because Hie smaller body had a relatively larger surface and lost more heat. It was found that for an average man of 11 stone engaged in business his diet should yield about 2800 calories. In fasting people were using up their own tissues. Protein was the great repair material, and formed the bulk of the soft tissues of all animals. At the same time it had a fuel value. Many attempts had been made to discover the best amount of protein to use. The figure of 100 grammes of dry protein bad been arrived at, and that was generally accepted. Probably more than 150 grammes would be considered dangerous. We all tended to take considerably more than the minimum of protein necessary, but that was advantageous, particularly '■ for brain work. The lecturer proceeded to discuss certain typical diets recommended, 1 illustrating his remarks from exhibits of f, foodstuffs "before him. Appetite and pleasurable sensation in eating had a real digestive value, and that gave a certain value to appetising materials that had no caloric value. The concluding portion of

the lecture was devoted to showing- the comparative caloric values of the most common foodstuffs at.their present prices, and to contradicting a <ew popular falIdcics. Mr J. H. Stephens proposed a hearty vote of thanks to the lecturer, the motion feeing seconded by Mr E. Gilkison and Carried Ip- acclamation*