Not always.
Her allergist was pleased that my 18-month-old was still mainly nursing. Turns out that she had many undiagnosed food and other allergies. She was instinctively avoiding most foods we were offering! Her allergies were not causing other symptoms like rashes but were keeping her and us up at night.
Her solid food intake increased upon allergy treatment and upon our learning the foods she could tolerate. She began to sleep a lot more soundly. I also quit eating those foods for the duration of breast feeding.
We went through that also. Everybody is different but it was easier for us to determine what the problem foods were once he was weaned.