A Summary and Analysis of the Major Contributions of
E.H. Ahrens, Jr. to the Field of Nutrition

The late 1940's and the 1950's were times of increasing awareness of the role that diet plays in the production of disease in man. During those years, the incidence of myocardial infarction and the prevalence of atherosclerosis were rising rapidly. Ahrens entered this exciting area of nutrition research after a period of training in analytical biochemistry under the direction of Donald Van Slyke and Lyman Craig at The Rockefeller Institute for Medical Research. Craig was one of the forerunners of the great period of separation science in biological chemistry. His use of countercurrent distribution for the separation of compounds led to the widespread use of chromatography. While Ahrens was in his apprenticeship with Craig, Moore and Stein began their epic work on the development of automated techniques of column chromatography for the separation of mixtures of amino acids. One cannot over-emphasize the importance of this type of careful analytical work which built bridges between clinical observations in nutrition and fundamental biochemical science and also served as a major force in ushering in the great period of molecular biology, beginning in the 1950's.

Ahrens first applied separation methodologies to the study of serum in patients with biliary cirrhosis. He always wielded a two edged knife in his analytical dissection of biologic problems. With one edge he described the nutritional status or disease status of the patient, and with the other, he utilized the best of laboratory science to unravel the puzzles of nature. In studying biliary cirrhosis, he analyzed a group of cases and wrote what is widely considered to be the seminal paper in modern research on that disease, naming biliary cirrhosis and fully describing it as a significant, separate clinical entity.  On the laboratory side, he noticed that individuals with biliary cirrhosis could carry large amounts of serum lipid and yet have translucent sera. In other conditions, there were many individuals with lesser concentrations of blood fat but with opalescent or turbid serum. He showed that the high phospholipid content in the sera of patients with biliary cirrhosis was responsible for the ability of the serum to carry a large amount of lipid without developing turbidity. This began his interest in the separation of biochemical classes of lipids in the serum.

With this keen interest in analytical technique, he utilized Lyman Craig's countercurrent distribution apparatus to perform the first clear separations of intestinal chyme during the process of digestion. The special role of partial glycerides and the rate of their formation was described in a classic paper in the Journal of Biological Chemistry. Likewise, he set our understanding of the chemical types of bile acids present in man on an exact chemical basis.

After refining methods for the separate analyses of serum phospholipids, triglycerides, cholesterol and its esters in plasma, he then began an examination of the effects of dietary fat on these components in the serum. It recently had been discovered that vegetable oils had different effects on serum lipid than animal fats. Ahrens performed elegant and exhaustively meticulous experiments demonstrating that the major factors were fatty acid chain length and unsaturation  regardless of animal or vegetable origin. He also showed that the fatty acids of the diet had a more profound effect on serum cholesterol levels than ingested cholesterol. To perform these studies, he developed the technique of formula feeding. He was among the first to demonstrate that human subjects could be kept in good physical condition by a totally synthetic diet made of simple components: a single fat, a single carbohydrate, and one source of protein, all reinforced with appropriate mineral and vitamin supplements. His work showed that the era of searching for new vitamins in food was coming to an end, since these synthetic diets of precisely known chemical composition were found to be fully adequate for the maintenance of health.

The formula diets derived by Ahrens enabled a precise dissection of the role of each dietary component on serum lipid levels. In his classic paper in the Lancet in 1957, which, in fact, became a Citation Classic, Ahrens showed the specific effects of chain length and of unsaturation of dietary fat on various serum lipid levels. In the course of these studies, he also showed that very high carbohydrate intake, or reduction of fat intake, could, in some individuals, provoke marked hyperlipemia. The hyperlipemia was characterized by a selective rise in triglyceride levels with relatively little change in cholesterol or phospholipid.

In order to pursue the chemical details of the effects of dietary fat, it became important to utilize the most modern analytical tool for the separation of fatty acids, much as had been done in earlier years for the separation of lipid classes by Ahrens and his colleagues. Thus, Ahrens and A.T. James built the first gas-liquid chromatograph for the separation of methyl esters of fatty acids in the U.S. Ahrens became a spokesman for the use of gas-liquid chromatography or GLC, to separate saturated and unsaturated fatty acids, and wrote an important manual for the use of GLC, which appeared as supplement to Nutrition Reviews.

During these years, Ahrens put his techniques of separation of fatty acid to good use in studies of human subjects with chyluria in whom recently absorbed fat appears quickly in the urine. He showed the specific effect of fatty acid chain length on the mode of absorption of fat: fats of short chain length appearing in the portal circulation and not in the cycle, whereas those with chain lengths greater than 10 or 12 appeared promptly in the chylous urine.

He then turned his attention to a series of studies on sterol balance in man. For the first time, in carefully controlled clinical settings, with subjects on formula diet, intricate analytic techniques were used to determine the rates of sterol synthesis as well as the formation of bile acids and secretion of sterol and bile acids. In a number of pioneering studies, he sketched the mode of operation of both drugs and diets in changing sterol balance in man. These studies were utilized and widely quoted in the development of the diet - heart disease hypothesis which has remained a compelling example of the linkage of human nutrition to disease.

In all of Ahrens' work, he took special cognizance of human variability. He foresaw the fact that genetic differences might require different dietary prescriptions for the maintenance of health or the prevention of disease. Never one to be swept into current fads, he always cautioned against dietary prescriptions for the entire national without full and fundamental facts being elucidated by the intensive study of small numbers of subjects.

His diligent application of laboratory science to the study of clinical problems, his unfailing conviction that clinical observation adds a major and essential ingredient to the understanding of disease, and his synthesis of these approaches in carefully engineered, replicable experiments, mark him as one of the great leaders of human nutrition in the last half of the century in this country. Although he no longer works in the laboratory, his energetic espousal of clinical research and nutrition remains undimmed. His book entitled The Crisis in Clinical Research is a landmark study of the status of clinical research in this country. It is widely used by educators and government officials in their planning of new undertakings in research on human disease.