This might seem like an obvious yes but I asked my Momma this question and she said that there are more nutrients in muscle but she isn't sure whether a fat humanoid would last longer than a muscular humanoid in a famine.
I think this comes down to pros and cons of each body type.
Fat has more energy, much more than glucose. Because of this, protein breakdown when it happens would be slower. And the brain can work on ketones and your heart basically works with ketones all the time. Ketosis is a longer process than protein breakdown and takes up most of the time that a human or other creature with similar metabolism is starving to death.
On the flipside, being fat increases your chance of having heart and liver failure. It also can lower your endurance and speed and while lowered speed is fine, if humanoids migrate, lowered endurance is the last thing you would want besides being attacked. Even without health problems, it still has downsides during migration.
Muscular humanoids have more strength and/or endurance. Both of these are positives. But protein breakdown is a relatively fast process and involves turning protein into glucose. So muscle mass, strength, and endurance would be lost. If this continues for too long, the humanoid will be down to the bone underweight and like being fat, this lowers endurance more than a low muscle mass would by itself. If a humanoid becomes underweight, it has a close to 0 chance of survival in a famine.
So given all these pros and cons, would a fat humanoid last longer due to ketosis or would a muscular humanoid last longer because of a lower chance of health problems, even at a higher than normal BMI?
These humanoids live in a grassland surrounded by forest. They also know how to grow plants. Usually both fruits and veggies from agriculture and animals to hunt are in abundance. Winter has a higher risk of famine because unless you have a greenhouse, only a few fruits and a few more veggies can survive winter. Animals to hunt can pretty much always survive winter. But if a supervolcano erupts, that can cause a global volcanic winter for a whole year. This would definitely have a high risk of famine.