Over the past few decades, diabetes has become a global pandemic with increasing threats to human health and global economies [1]. According to Diabetes Atlas of International Diabetes Federation, 537 million adults worldwide are living with diabetes predominately type 2 diabetes (T2D) in 2022. Currently the most effective strategy for prevention and management of T2D is modification of lifestyle and diet [2]. Nutritional intervention for T2D is associated with improved health outcomes and reduced healthcare cost [3, 4]. Reduced food intake, while avoiding malnutrition, could ameliorate T2D, aging and many other metabolic disorders in numerous species including invertebrate model organisms, rodents, primates, and humans [5], [6], [7], [8], [9], [10]. The ratio of macronutrients in diet also plays an important role. It has been reported that longevity and metabolic health were achieved by replacing protein with carbohydrate in a carbohydrate replacement diet [11], which suggested that restriction of protein consumption may bring about health benefit to the body.

Dietary interventions at daily basis such as calorie restriction, low-protein diets, time-restricted feeding, intermittent fasting, alternate-day fasting and long-term fasting might not be feasible for most subjects due to the difficulty to adhere to dietary instructions or the difficulty of drastically changed lifestyles which might cause detrimental effects [12], [13], [14], [15], [16], [17]. To minimize the burden of chronic dietary intervention, periodic use of different kinds of fasting-mimicking diet (FMD) has been proposed to treat T2D [18, 19]. Use of 4-cycle FMD (low in calories, sugars, and protein but high in unsaturated fats) was found to alleviate T2D and aid in the regeneration of insulin-producing β cells via Neurog3 expression [18]. We recently explored a new strategy, i.e., intermittent protein restriction (IPR) for diabetes intervention [20]. Briefly, we first found that IPR with 5% of dietary protein for 3 days each week was effective in improving hyperglycemia in a streptozotocin (STZ)-induced diabetes mouse model. A 3-2-2 diet (low-protein diet for 3 days, followed by a high-protein diet for 2 days and normal chow for 2 days) was then designed as an effort to quickly restore the protein level in the mice following the use of a low-protein diet. The dietary intervention with the 3-2-2 diet performed slightly better than a 3-4 diet (low-protein diet for 3 days, followed by normal chow for 4 days) in improving hyperglycemia in diabetic mouse models [20]. Obese Zucker diabetic fatty (ZDF) rats have metabolic abnormalities such as hyperinsulinemia, hyperlipidemia and hypertension, along with impaired glucose tolerance. ZDF rats have been used as a diabetes model as the rats develop serious T2D under high-fat diet conditions due to homozygous mutation (fa/fa) of the leptin receptor gene. In this study, we investigated whether IPR is effective in T2D intervention in ZDF rats in an effort to extend our previous findings in mouse models. Furthermore, we performed single-cell RNA sequencing with the islets and identified distinct β cell profiles associated with T2D in ZDF rats.