To eat on the Sabbath the same amount of food eaten on a working day, is entirely out of place. The Sabbath is the day set apart for the worship of God, and on it we are to be specially careful in regard to our diet. A clogged stomach means a clogged brain. Too often so large an amount of food is eaten on the Sabbath that the mind is rendered dull and stupid, incapable of appreciating spiritual things. The habits of eating have much to do with the many dull religious exercises of the Sabbath. The diet for the Sabbath should be selected with reference to the duties of the day on which the purest, holiest service is to be offered to God.  Review and Herald, May 27, 1902

We should not provide for the Sabbath a more liberal supply or a greater variety of food than for other days. Instead of this the food should be more simple, and less should be eaten, in order that the mind may be clear and vigorous to comprehend spiritual things.

Overeating befogs the brain. The most precious words may be heard and not appreciated, because the mind is confused by an improper diet. By overeating on the Sabbath, many have done more than they think to dishonor God.  Testimonies For the Church, vol. 6, 357 

By overeating on the Sabbath, many do more than they think, to unfit themselves for receiving the benefit of its sacred opportunities.  Counsels on Diet and Foods, 46 

The Sabbath of the Lord is a day of rest from labor; and the diet upon that day should be more simple, and partaken of in less quantities, than upon the six laboring days, because we do not have that exercise upon the Sabbath that we have upon the other days of the week. Many have erred in not practicing self-denial upon the Sabbath. By partaking of full meals, as on the six laboring days, their 1) minds are beclouded; 2) they are stupid, and 3) often drowsy; 4) some suffer with headache. 5) Such have no truly-devotional feelings upon the Sabbath, and the blessing resting upon the Sabbath does not prove a blessing to them.  The Spirit of Prophecy, vol. 1, 226