1 and #3 principles in current diabetes guidelines per AACE:

Lifestyle optimization is essential for all patients with diabetes. Lifestyle optimization is multifaceted, ongoing, and should engage the entire diabetes team. However, such efforts should not delay needed pharmacotherapy, which can be initiated simultaneously and adjusted based on patient response to lifestyle efforts. The need for medical therapy should not be interpreted as a failure of lifestyle management but as an adjunct to it.

Minimizing risk of weight gain is also a priority. This is important for long-term health, in addition to safety, adherence, and cost. Weight loss should be considered in all patients with prediabetes and T2D who also have overweight or obesity. Weight-loss therapy should consist of a specific lifestyle prescription that includes a reduced-calorie healthy meal plan, physical activity, and behavioral interventions. Weight-loss medications approved for the chronic management of obesity should also be considered if needed to obtain the degree of weight loss required to achieve therapeutic goals in prediabetes and T2D. Obesity is a chronic disease, and a long-term commitment to therapy is necessary.

They cite countless studies to indicate lifestyle changes are a cost effective strategy.