Insulin does not spike if the fruit in question is whole fruit. Unlike honey, cane sugar, high-fructose corn syrup and other forms of sugar that are added to many processed foods, the sugar naturally found in fruit is consumed in the company of fiber, which helps your body absorb the sugar more slowly.
When you consume a food or beverage that contains carbohydrates, your digestive system breaks the carbs down into a type of sugar called glucose, which enters the bloodstream. When blood sugar levels rise, the pancreas produces the hormone insulin, a signal to your cells to absorb the glucose so it can be used immediately as energy or stored in the liver and muscles for later use. Repeatedly eating foods that cause surges in blood sugar makes the pancreas work harder. Over time, that can lead to insulin resistance and an increased risk of Type 2 diabetes.
Refined grain products like white bread, crackers, and cookies, which tend to be low in fiber, deliver large amounts of carbohydrates per serving and are digested very quickly, raising blood sugar and insulin levels. Sugars enter into the bloodstream especially rapidly when you consume carbohydrates in liquid form, such as in sugary sodas, juices.
But it’s not as simple as adding fiber to starchy foods or soda — the quality and physical form of carbohydrates are critical, which means favoring whole foods over processed foods and added sugars. That includes favoring whole fruit over fruit juice: Fruit juices can contain fiber, but some of that fiber is broken down in the juicing process, reducing the metabolic benefit compared with intact fruit.
To minimize spikes in insulin, it’s best to eat fruit whole. That’s because with whole fruit the cell walls remain intact, this is how fiber can offer the greatest benefit, because the sugars are effectively sequestered within the fiber scaffolding of the cells, and it takes time for the digestive tract to break down those cells. Four apples may contain the same amount of sugar as 24 ounces of soda, but the slow rate of absorption minimizes the blood sugar surge.