The straight answer, up front

If you want the short version:

Yes, your energy needs fall — usually by somewhere between 400 and 1,200 kilojoules a day, and more if you were physically active at work or you drop your activity once you retire.

But your protein needs go up, not down. Older adults need more protein per kilogram of body weight than young adults, not less.

And your needs for calcium, vitamin D, vitamin B12 and fibre all stay the same or increase, at exactly the moment your appetite tends to shrink.

So the phrase to hold onto is this: eat less food, but better food. Same volume on the plate, more nutrients per mouthful. That's the whole strategy in one sentence.

Seven rules that work in a camp dining room

1. Walk the whole room before you pick up a plate. Thirty seconds. See what's actually good. Otherwise you fill up on the first thing you see and then go back for the thing you actually wanted.

2. Use the smaller plate if there are two sizes. This is the single highest-yield change in any buffet, and it costs nothing.

3. Protein and vegetables fill the plate first. Two-thirds of the plate. Then, if you still want it, the starch. Not the other way around.

4. Take one plate. Sit down. Wait ten minutes before deciding on seconds. You will almost never want them. The urge to go back is fastest in the first five minutes and it fades.

5. Dessert is a decision, not a default. Decide before you walk in whether tonight is a dessert night — not every night, not never. A rule you set in advance beats a decision you make while standing in front of a chocolate fountain.

6. Don't eat in your room. The room is for sleeping. Eating there is how a bag of shapes becomes a nightly ritual you didn't consciously choose.

7. Fill your water bottle before you go to the dining hall, not after. Hydration first, then food