Why are lipids generally a poorer nutrient source than carbohydrates despite containing more energy?

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The main idea is that energy release depends on both how much energy a nutrient can provide per gram and how quickly and easily the organism can access and metabolize it. Lipids pack a lot of energy per gram, but they are hydrophobic and poorly soluble in water, which makes uptake and processing slow. They must be emulsified and hydrolyzed by lipases to break triglycerides into fatty acids and glycerol, and then fatty acids need activation and beta-oxidation before ATP can be produced. This multi-step, slower pathway means energy from lipids is released more slowly than from carbohydrates, which are water-soluble and readily transported into cells and funneled directly into glycolysis and the energy-yielding pathways. So, despite higher energy per gram, lipids are a poorer immediate nutrient source because their accessibility and rate of metabolism are limited.