It is from this article.
Get ready to pack in the protein, healthy fats, and fiber.
Does it mean to include?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
to pack in a lot of [fiber, etc.]
means: to add those items to your diet (here, your breakfast) or the food you eat/make.
What Is a Good, Nutritious Breakfast? Get ready to pack in the protein, healthy fats, and fiber
Taken from the OP's link.
It is not the best English.
And for especially badly written English, it could mean: eat a lot of fiber etc.
To pack things in somewhere is to put in as much (or as many) of things as you can. You can pack a lot of clothes in a suitcase if you push them hard. To pack protein, healthy fats, and fiber (or fibre) into yourself means to eat a lot of foods containing these things.
pack verb (FILL) [ T ] to fill a space, or to crowd people or things together, esp. in large numbers: