Good Calories, Bad Calories

By 1955, Pete Ahrens at Rockefeller University had come to this same conclusion, although Ahrens was specifically studying triglycerides, rather than the VLDL particles that carry the triglycerides. Ahrens was considered by many investigators to be the single best scientist in the field of lipid metabolism. He had observed how the triglycerides of some patients shoot up on low-fat diets and fall on high-fat diets. This led Ahrens to describe a phenomenon that he called carbohydrate-induced lipemia (an excessive concentration of fat in the blood). When he gave lectures, Ahrens would show photos of two test tubes of blood serum obtained from the same patient—one when the patient was eating a high-carbohydrate diet and one on a high-fat diet. One test tube would be milky white, indicating the lipemia. The other would be absolutely clear. The surprising thing, Ahrens would explain, was “that the lipemic plasma was obtained during the high-carbohydrate period, and the clear plasma during the high-fat regimen.” (Joslin had reported the same phenomenon in diabetics thirty years earlier. “The percent of fat” in the blood, he wrote, “rises with the severity of the disease…and is especially related to the quantity of carbohydrate, which is being oxidized, rather than with the fat administered.”)

Over the course of a decade, Ahrens had seen only two patients whose blood serum became cloudy with triglycerides after eating high-fat meals. He had thirteen in whom carbohydrates caused the lipemia. Six of those thirteen had such high triglycerides that they had originally been referred to Ahrens from physicians who had misdiagnosed them as having a genetic form of high cholesterol. Since the VLDL particles that transport triglycerides, as Gofman had noted, also carry cholesterol and so contribute to the total cholesterol in the circulation, an elevated triglyceride level can elevate total cholesterol along with it. Ahrens believed that the fat-induced lipemia was a rare genetic disorder but the carbohydrate-induced lipemia was probably “an exaggerated form of the normal biochemical process which occurs in all people on high-carbohydrate diets.” In both cases, the fat in the blood would clear up when the subjects went on a low-calorie diet. To Ahrens, this explained why the carbohydrate-induced increase in triglycerides was absent in Asian populations living primarily on rice. As long as they were eating relatively low-calorie diets compared with their level of physical activity, which was inevitably the case in such impoverished populations, the combination would counteract the triglyceride-raising effect of the carbohydrates.

The critical question was whether prolonged exposure to an abnormally high triglyceride level increased the risk of atherosclerosis. If carbohydrate-induced lipemia was as common as Ahrens believed, “especially in the areas of the world distinguished by caloric abundance and obesity,” then it was important to know. If so, then having patients with high triglycerides eat less fat would only make the condition worse. By 1957, Ahrens was also warning about the dangers of oversimplifying the diet-heart science: maybe fat and cholesterol caused heart disease, or maybe it was the carbohydrates and triglycerides. “We know of no solid evidence on this point,” wrote Ahrens, “and until the question is further explored we question the wisdom of prescribing low-fat diets for the general population.”