No Low-Fat Diet for the Failing Heart?

Chances are that everyone knows about the heart’s oxygen requirement, but few would consider the heart’s metabolism of energy-providing substrates a big issue. Since the celebrated work of C. Lovatt Evans and Ernest Starling1,2 at the beginning of the last century, physiologists have recognized the heart as an efficient transducer of energy. Like an engine, the heart turns chemical energy into mechanical energy, efficiently and at a high rate. Metabolism of energy-providing substrates and contractions of the heart are tightly coupled.3 Because the heart’s energy for contraction is derived from oxidative phosphorylation of adenosine diphosphate to adenosine triphosphate, myocardial oxygen consumption is also commonly used to measure cardiac efficiency.4 Another feature of the heart is also worth mentioning. The heart is a metabolic omnivore, and for any given environment it uses the most economic fuel available5 (Figure). In the fasted state, when the fatty acid levels are high, the heart oxidizes predominantly fatty acids.6 Metabolic adaptability comes into play when the heart is stressed and veers toward carbohydrate oxidation. With a short-term increase in workload, the working heart ex vivo covers its increased need for energy through the oxidation of glycogen, lactate, and glucose, in that order.4 For a given amount of oxygen used, the heart in vivo performs up to 40% more efficiently with glucose than with fatty acids as the main energy-providing substrate.7 In a simulated state of exercise, the heart spares glycogen and oxidizes lactate …