If the fat can be mobilized from the adipose tissue with “sufficient effectiveness,” Pennington suggested, “no calorie restriction would be necessary” on a carbohydrate-restricted diet. A greater share of the energy needs would be supplied by the calories from the fat tissue, and the appetite would naturally adjust. “Weight would be lost, but a normal caloric production would be maintained.” A person would be eating less because his appetite would be reduced by the increased availability of fat calories in his circulation, not because the diet somehow bored, restricted, or revolted him. He would be eating less because his fat tissue was shrinking; his fat tissue would not be shrinking because he was eating less. “The result would appear to be a ‘negative energy balance,’” Pennington said, “because so much of the energy needs would be supplied from stored amounts.”

Energy expenditure would also increase on such a diet. The now unconstrained flow of fat calories from the adipose tissue would increase the fuel available for cellular metabolism. The cells would no longer be undersupplied, as though living in a constant state of semi-starvation, and their metabolism would no longer be inhibited. Metabolic rate would increase, as would the impulse to physical activity—the urge to expend some of the energy now freely available. That such an effect is possible in humans, Pennington said, had been one of the observations reported by Du Bois and his colleagues in their yearlong all-meat-diet experiment with Stefansson and his colleague Anderson. These investigators had measured Stefansson’s and Anderson’s metabolism on a balanced diet and then measured their metabolism repeatedly during the yearlong trial. Both men lost some weight while eating the meat diet; both increased their basal-metabolic rate—7 percent for Stefansson and 5 percent for Anderson. Such an increase in energy expenditure could account for a weight loss of twenty pounds or more over the course of a year. If this change in expenditure went in the other direction when the diet included carbohydrates, it could easily account for the slow development of obesity.

When the obese or overweight go on a carbohydrate-restricted diet, Pennington theorized, there will be an increase in metabolic and physical activity as their bodies expend this newly available energy, and an attendant weight loss. The naïve assumption would be that the physical activity caused the weight loss, and it would be wrong. They will finally be burning off their accumulated fat stores and putting that energy to use.

Under these conditions, the energy expenditure of the obese individual might rise to what it otherwise would have been in a healthy state. It was not out of the question, as Frank Evans had reported and Sidney Werner had speculated, that this might be more than four thousand calories a day for someone who was definitively obese. Such an individual might easily eat over three thousand calories a day and still lose a pound or two a week.