Our elders were much wiser than we are, giving advice:
Breakfast like a king,
Lunch like a citizen,
Dine like a pauper.
While sailing-cruising one should live by this advice even more.
There are many opportunities to exercise on board, one only has to think about open mindedly about one's opportunities. The "going to the gym" caper is an over rated self denying excuse.
On a boat the opportunity to exercise might not be obvious but nevertheless is there.
The dinghy or kayak is one (not after dinner but instead of!), the anchor is a perfect weight to lift, gymnastics is another one with sit ups, stand ups, push and pull ups never mention yoga which only needs determination.
It is not to build huge muscles just keep one's body pliable so when we have to bend that heavy jib we don't end up with pulled muscles, torn ligaments, bad backs.
There is no valid reason to grow old and also grow fat. There is no medical reason either.
It is down to our screwed up values and lifestyle that the above advice is - literally - turned upside down. Strewth!
We leave home with next to nothing under the belt, run all day long on a sandwich dreaming of dinner when we fill ourselves way over necessity just because we were mentally torturing ourselves dreaming of food all day. Then we go to bed with 2000 calories in our stomachs, could not rest properly while digesting the crap we ate and waking in the morning tired, exhausted, pissed off and late and likely with a bad heartburn, so we don't eat breakfast again. Crazy!
Then, we go cruising and carry our screwed lifestyle aboard drinking excessively in the bargain.
The body works differently. If one has a good breakfast it is going to be burned up by the day's activities while the dinner is going to end up as fat reserve around one's waistline, no matter what, dry land or aboard.