Vitamin D deficiency increases risk of type 2 Diabetes.

This study investigated whether baseline vitamin D level is associated with the incidence of type 2 diabetes in high-risk subjects for up to 5 years of follow-up, independently of obesity, baseline insulin resistance, and β cell function. Participants were 1080 nondiabetic Korean subjects based on the presence of one or more risk factors for type 2 diabetes, including obesity, hypertension, dyslipidemia, and/or family history of type 2 diabetes. Of the participants, 10.5% had a serum vitamin D deficiency (<10 ng/mL), 51.6% had an insufficiency (10.0-19.9 ng/mL), and 38.0% had a sufficiency (≥20 ng/mL), and the incidence of type 2 diabetes at 32.3 months declined accordingly: 15.9%, 10.2%, and 5.4%, respectively. After adjustment for age, sex, blood pressure, lifestyles, family history, season, parathyroid hormone, and high-sensitivity C-reactive protein, the participants with vitamin D deficiency had an increased risk of type 2 diabetes (106% increase for vitamin D levels 10-19.9 ng/mL compared with ≥20 ng/mL and 223% for vitamin D level <10 ng/mL compared with ≥20 ng/mL) independently of BMI, HOMA2-IR, and insulinogenic index. The authors conclude "The current prospective study suggests that vitamin D metabolism may play a role in type 2 diabetes pathogenesis independently of known risk factors".

Lim S, Kim MJ, Choi SH, Shin CS, Park KS, Jang HC, Billings LK, Meigs JB. Association of vitamin D deficiency with incidence of type 2 diabetes in high-risk Asian subjects. Am J Clin Nutr. 2013 Mar;97(3):524-30.

Omega-3 promotes weight loss.

 This study investigated whether supplementation with omega-3 alone, then consumed together with a very low calorie diet (VLED), facilitated weight loss, improvements in blood lipids and positive changes to inflammatory mediators. For 4 weeks of prior supplementation, one group consumed 6 × 1 g capsules per day monounsaturated oil (placebo), the other group consumed 6 × 1 g capsules per day of fish oil each comprising 70 mg EPA and 270 mg DHA, while consuming their usual diet. Each group continued with their supplements for another 4 weeks while both groups followed a VLED regimen. At 4 weeks levels of EPA and DHA doubled in the fish oil group, with no significant changes to anthropometric measurements for either group. At 8 weeks a significant reduction in weight and BMI with a greater percentage decrease for females was seen in the fish oil group compared to placebo.

Note that the dose of 2040mg combined EPA/DHA is not achievable through diet. You'll need a high quality supplement.

Munro IA, Garg ML. Prior supplementation with long chain omega-3 polyunsaturated fatty acids promotes weight loss in obese adults: a double-blinded randomised controlled trial. Food Funct. 2013 Apr 25;4(4):650-8.