Hello, Solid could also mean here " consistent"

Have to disagree with Neal and Jura here. 'Stodgy' is an adjective that would describe food like meat and potatoes that - as Jura says, sit in your stomach for a long time - but it doesn't make much sense to coordinate 'stodgy' with 'unchanging' in the same clause - the first doesn't obviously 'expand' on the meaning of the second unless you corrupt the meaning to fit that interpretation. Here also is one of the most important lessons in learning a language: native speakers will often disagree as to what things mean, and what is correct!!

Meat & potatoes fill you up & sit in your stomach for a long time. Solid here can mean 'filling'. I would agree with Neal that it's a sweeping statement as a lot of European countries base their meals around meat & potatoes as well.

'Solid' here means the same as 'unchanging' = stable. This pattern of using two different adjectives to describe one quality is quite common in English, and if you can recognise it helps you guess the meaning of either one of the words in the pair that you don't know. For example, There is no life on the moon. It is barren and infertile. Here 'barren' and 'infertile' are synonyms, like 'solid' and 'unchanging'. The purpose of using this pattern is usually to add emphasis - it makes the point in a stronger way than just using one adjective alone.

Hi Cindy In your sentence, solid refers to the quality of the food, not the fact that it does not change much, and to expand on, rather than emphasise, the unchanging nature of the diet. Here, solid is 'mundane' or 'stodgy'; meat and potatoes weighing heavily on the stomach compared to, say, salad, fruit or a more varied diet. Without further context or evidence this appears to be a somewhat sweeping generalisation - it might be true, but I have never heard of the American diet referred to in this way.