21 C.F.R. § 105.66 : Food and Drugs — FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES — FOOD FOR HUMAN CONSUMPTION — FOODS FOR SPECIAL DIETARY USE — LABEL STATEMENTS — Label statements relating to usefulness in reducing or maintaining body weight

(a) General requirements. Any food that purports to be or is represented for special dietary use because of usefulness in reducing or maintaining body weight shall bear:
(1) Nutrition labeling in conformity with §101.9, or, where applicable, §101.36 of this chapter, unless exempt under that section; and
(2) A conspicuous statement of the basis upon which the food claims to be of special dietary usefulness.
(b) Nonnutritive ingredients.
(1) Any food subject to paragraph (a) of this section that achieves its special dietary usefulness by use of a nonnutritive ingredient (i.e., one not utilized in normal metabolism) shall bear on its label a statement that it contains a nonnutritive ingredient and the percentage by weight of the nonnutritive ingredient.
(2) A special dietary food may contain a nonnutritive sweetener or other ingredient only if the ingredient is safe for use in the food under the applicable law and regulations of this chapter. Any food that achieves its special dietary usefulness in reducing or maintaining body weight through the use of a nonnutritive sweetener shall bear on its label the statement required by paragraph (b)(1) of this section, but need not state the percentage by weight of the nonnutritive sweetener. If a nutritive sweetener(s) as well as nonnutritive sweetener(s) is added, the statement shall indicate the presence of both types of sweetener, e.g., "Sweetened with nutritive sweetener(s) and nonnutritive sweetener(s)."
(c) "Low calorie" foods. A food purporting to be "low calorie" must comply with the criteria set forth for such foods in §101.60(b)(2) and (b)(3) of this chapter.
(d) "Reduced calorie" foods and other comparative calorie claims. A food purporting to be "reduced calorie" or otherwise containing fewer calories than a reference food must comply with the criteria set forth for such food in §101.60(b)(4) and (b)(5) of this chapter.
(e) Label terms suggesting usefulness as low calorie or reduced calorie foods.
(1) Except as provided in paragraphs (e)(2) and (e)(3) of this section, and in §101.13(q)(2) of this chapter for soft drinks, a food may be labeled with terms such as "diet," "dietetic," "artificially sweetened," or "sweetened with nonnutritive sweetener" only if the claim is not false and misleading, and the food is labeled "low calorie" or "reduced calorie" or bears another comparative calorie claim in compliance with part 101 of this chapter and this section.
(2) Paragraph (e)(1) of this section shall not apply to any use of such terms that is specifically authorized by regulation governing a particular food, or, unless otherwise restricted by regulation, to any use of the term "diet" that clearly shows that the food is offered solely for a dietary use other than regulating body weight, e.g., "for low-sodium diets."
(3) Paragraph (e)(1) of this section shall not apply to any use of such terms on a formulated meal replacement or other food that is represented to be of special dietary use as a whole meal, pending the issuance of a regulation governing the use of such terms on foods.
(f) "Sugar free," and "no added sugar." Criteria for the use of the terms "sugar free" and "no added sugar" are provided for in §101.60(c) of this chapter.

21 C.F.R. § 105.66

58 FR 2430, 1/6/1993