A high carbohydrate, low fat diet was once the standard weight loss diet prescription. Unfortunately such a diet may increase multiple risk factors for heart disease, probably due to low levels of essential fatty acids.
A study out of Sichuan University showed that a high carbohydrate, low fat diet (presumable a high grain diet) lowered both HDL and LDL cholesterol, and increased insulin, triglycerides, BMI and waist circumference.
The increase in triglycerides and waist circumference indicates an increase in insulin resistance…which correlates with the increase in plasma insulin levels. It is possible that a small increase in omega-3 and monounsaturated fats would have prevented the increase in insulin resistance.