Prevention highlights the expertise of Thomas Russo on dietary staples recommended to boost immune response to illness. Russo recommended taking it slow with bland foods such as toast when battling digestive illnesses. Above all, he notes that hydration should be the priority. If you're dealing with an upset stomach, he recommends taking small sips of water to avoid overloading your GI tract at once. Sports drinks can also help give you electrolytes to increase your energy levels, he said.