[function_seven]

I think it's the opposite of pedantic. They're asking "where" the weight goes. It does not transmutate into motion. The weight has to go somewhere.

Pee, poo, breath, sweat, snot, earwax, hair, nails, spit?

I assumed the CO2 we exhale would be the largest portion, and the article backs that up.

[luhn]

But mass can be converted into energy. Obviously that's not the primary weight loss driver (what a metabolism that would be!), but it certainly doesn't break the laws of physics.

EDIT: Because I was curious, I did the math.

Assuming diet of 2000kCal per day.

2000kCal / 3500kcal/lb fat = 0.5714 lb fat = 0.259kg fat

0.259kg = 2.329×10^16 joules = 5.556megatons of TNT

5.556megatons/day / 24 hours / 60 minutes / 60 seconds = 0.000064megatons/second = 64 tons of TNT per second

Less than I thought actually, but not someone you'd want to hang out with.

[function_seven]

Mass cannot be changed into energy. Maybe it can down the hall in Mr. Einstein's physics class, but here in my nutrition class we will not violate the classical laws of the universe.

[marton78]

Mass is converted to energy by every chemical reaction! Say you have a mixture of rust and aluminium powder, which you ignite (the thermite reaction). It results in iron, aluminium oxide and heat. The resulting matter will weigh a tiny bit less, by exactly the energy produced divided by c^2

[dTal]

The real pedantry is in the comments.

On the patented Special Relativity Diet, by eating nothing and converting your rest mass to energy, you can lose... a whopping 93 nanograms a day!