Eli5 So we need calories to survive. If there are 100 calories in a spoon of oil, how come we can’t survive on oil for emergencies?

Question

Eli5 So we need calories to survive. If there are 100 calories in a spoon of oil, how come we can’t survive on oil for emergencies?

In: 3554

Answer 1

Others have mentioned micronutrients, amino acids etc. I just want to add one more important point about sugar:

Sugar is fairly important for the body’s functioning. It is possible to survive without it, but this can cause problems.

The body can get sugar in several ways. It can be eaten. Starches can be broken down for it. A reserve of sugar in the liver can be broken down. If there are no sugar or starches in the diet, then the body can use the *energy* from oils combined with the *carbon* from proteins to make sugar. If the body is only getting oils, it uses muscle mass to get the carbon. When the body runs of of muscle mass that it can use, then it can no longer make sugar even with lots of oils.

The not ELI5 explanation for this is that fatty acids are oxidized into 2-carbon acetyl thioesters which cannot be turned into pyruvate without first going into the Krebs cycle. Here they must be converted to malate first which loses 2 carbons for every 2 carbons that goes into the cycle. Gluconeogenesis from only fatty acid substrates depletes Krebs intermediates.

Now the body can still survive without the sugar, but it must make toxic acids and ketones in order to keep the brain alive. There is some debate and controversy about how harmful this is.