Effect of Partial Dietary Replacement from Animal to Plant-Based Protein for Type 2 Diabetes Management

The goal of this clinical trial is to examine the effect plant-based diet, with a partial replacement of animal protein by plant protein, in blood sugar levels and other health risks of people with type 2 diabetes and excessive weight. The plant-based diet will be compared to a standard healthy diet according to guidelines for people with diabetes. Participants will follow a plant-based or a standard healthy diet for 24 weeks and will maintain their habitual levels of physical activity.

This is a single center, open label, parallel and randomized clinical trial. Subjects with type 2 diabetes (T2D) and excessive weight will be recruited through advertisement on the web page of Hospital de Clínicas de Porto Alegre (HCPA), local newspaper, television and social media, or referred by a doctor or nutritionist, from external to HCPA services. Patients will be also screened through electronic records of HCPA's clinics. After screening and selection according to inclusion criteria, participants will undergo a clinical, laboratory and nutritional evaluation following a standard assessment protocol. After all baseline assessments, they will be randomly allocated to one of the following interventions for 24 weeks: (1) Control diet (CDG): hypocaloric diet according to current guidelines for T2D or (2) Plant-based diet (PBG): hypocaloric diet with partial replacement of animal protein by plant protein. Both groups will have caloric targets calculated to achieve a 5% weight loss during the 6 months of study, will have the same macronutrient distribution on the diet and will receive the same nutritional and medical support. Telephone calls will be performed monthly for adherence evaluation. At the end of 12 and 24 weeks of intervention, all patients will be submitted to the same clinical, laboratory and nutrition exams applied at baseline.

Eligibility Criteria:
Inclusion Criteria:

* Adults (≥18 and ≤65 years old)
* Diagnosis of Type 2 Diabetes;
* Glycated hemoglobin from 7% to 11%;
* Overweight or obesity (BMI ≥25 kg/m² and \<40 kg/m²);
* Use of any hypoglycemic and insulin;
* Stable weight (maximum variation of approximately 5%) for at least 12 weeks before screening;
* Not having undergone dietary intervention in the last 6 months;
* Have the ability to understand and be able to adhere to intervention proposals;
* Able and willing to provide an informed consent form for written and to comply with the requirements of the study protocol;

Exclusion Criteria:

* Type 1 diabetes mellitus;
* Retinopathy with vision deficit that limits the activities proposed in the interventions;
* Chronic kidney disease with estimated glomerular filtration \< 30 mL/min per 1.73m²;
* Liver failure, chronic viral hepatitis;
* Grade III or IV heart failure
* Active or progressive neurodegenerative disease;
* Prior stroke that has caused sequelae;
* Use of medications that affect glucose metabolism (e.g. corticosteroids or immunosuppressants) or cause weight loss;
* Chronic treatment with oral or parenteral corticosteroids (\>7 days consecutive treatment) within 4 weeks prior to screening;
* Treatment with weight-reducing agents (eg, orlistat, sibutramine, topiramate, bupropion, liraglutide, semaglutide) within the last 12 weeks before screening;
* Treatment with thyroid hormone that was not maintained at a stable dose in last 12 weeks before screening;
* History of active substance abuse (including alcohol) within the last year;
* Thyroid Stimulating Hormone (TSH) outside the normal range;
* Fasting triglycerides ≥ 600 mg/dL;
* Tumor diagnosed and/or treated (except basal cell skin cancer, carcinoma in situ of the cervix, or prostate cancer in situ) within the last 5 years;
* Severe psychiatric illness;
* Predisposition or diagnosis of eating disorders;
* Women who are pregnant, intend to become pregnant during the study period, or who are currently breastfeeding;
* Hyperglycemia characterized by acute symptoms: polyuria, polydipsia and/or weight loss in the last 3 months;
* Metabolic and acute complications of diabetes such as ketoacidosis or hyperosmolar coma;
* Potentially unreliable patients and those deemed by the investigator to be unsuitable for the study;
* Night workers who work after 10pm;
* Being on a vegetarian, vegan or flexitarian diet at the time of recruitment;
* Having undergone bariatric surgery;
* Carriers of the human immunodeficiency virus (HIV);
* Any other medical condition/disorder that the investigators consider that are likely to: interfere with the patient's ability to complete the entire study period or participate in study activities;
* Participants who require any treatment that could affect the interpretation, reliability or safety of data during the study intervention.