Potato, potahto? It turns out it all depends on how that potato (or potahto) is cooked. Did you know that the way we cook our food can significantly alter its nutritional value? From grilling and baking to boiling and microwaving, the cooking method we choose can impact the nutrient content, texture, and flavor of our meals. This includes the food’s effect on blood sugar levels. In this blog, we will explore six different ways cooking can affect the nutritional value of our food and the blood sugar response.
Boiling is a common cooking method that involves immersing food in hot water until it becomes soft and tender. It is one of the cooking methods in which the greatest amount of nutrients are lost. Boiling can cause water-soluble vitamins (vitamins C and B) to leach out into the cooking water, leading to a loss of nutrients. This impacts foods like broccoli and spinach, which are commonly boiled and can lose up to 50% of their vitamin C in the process. However, we can retain the nutrients lost during the boiling process if we use the cooking water as a broth or soup base.
One of the positives of boiling our food is that it destroys the greatest amount of antinutrients. Antinutrients (phytates, tannins, lectins, and oxalates) are compounds derived from plants that hinder the body’s ability to absorb nutrients. The good news is, antinutrients are not a concern for the majority of the population. They are primarily an issue for those who are malnourished or eat a diet comprised of exclusively uncooked plant foods. For the rest of us, the benefits of eating vegetables far outweigh the negative impact of any antinutrients.
Pasta, potatoes, and rice are all starchy carbohydrates that usually cause a spike in blood sugar levels. However, there are cooking methods that can allow us to eat the same food with a reduced rise in blood glucose levels. This process involves turning starchy carbohydrates into resistant starches.
Starch is a type of carbohydrate and is composed of multiple glucose molecules connected together. Raw, starchy foods have a highly ordered structure, making them difficult for the body to digest. However, heating them in water (like boiling rice) weakens this structure, making it easier for the body to quickly pull apart each glucose molecule, absorb the glucose, and increase blood sugar levels. This is why cooked, starchy foods like rice, pasta, and potatoes spike our blood sugar rapidly.
However, leftovers are a game changer. When we take that leftover pasta and put it into the fridge, it cools and the structure can reorganize itself. This reorganization turns the pasta into a “resistant starch.” Resistant starches are a form of carbohydrate that is not easily broken down by the body (much like a fiber). The presence of resistant starches is why the next day, chilled pasta does not spike blood sugar to the same extent as last night’s heated spaghetti.
If you’re not a fan of cold leftovers then we have great news for you. Recent research has shown that reheating these resistant starches is even better! Researchers are not entirely sure why it works but reheating the leftovers lowers the blood sugar response even more. We need more studies to show the optimal heating, cooling, and reheating time and temperatures, but as soon as more studies are conducted on this topic, we will keep you informed.
Starchy foods that can be turned into resistant starches by cooling and/or reheating include potatoes, rice, pasta, barley, peas, lentils, and beans.
Steaming is a popular method for cooking vegetables, fish, and other foods. It involves exposing the food to steam instead of boiling it in water. Steaming preserves the nutrients in the food, including antioxidants and vitamins, and it can help retain the natural flavors and textures of the food. It is an excellent method for people who are concerned about their blood sugar levels, as it doesn't add any oil or fat to the food.
Steaming slightly reduces the nutrient content of certain foods. This primarily pertains to water-soluble vitamins since these are the vitamins that are sensitive to heat and water. However, steaming does not cause a loss of vitamins to the same extent as boiling. Research has shown that steaming broccoli and spinach in particular only reduced the vitamin C content by 9 to 15%.
Grilling involves cooking food over an open flame or hot coals. It is a quick and easy way to cook meats and vegetables. The heat from the BBQ will bring out a smoky flavor and the caramelization will help to enhance the food’s natural flavors. Grilling is one of the best ways to preserve the food’s nutritional value. The lack of added oils or dressings makes it a clean cooking option.
However, dry-heat cooking like grilling, frying, or baking can cause the production of advanced glycation end products (AGEs). High levels of AGEs have been associated with inflammation and insulin resistance. Insulin resistance is a precursor for metabolic conditions and prediabetes. To minimize the amount of AGEs, choose boiled eggs instead of fried eggs, poached chicken in place of grilled chicken, or beef stew instead of grilled steak. These substitutions are of greater importance for meat products. Plants do not contain as many AGEs.
Baking involves cooking food in an oven, either by dry heat or by adding moisture, such as with a marinade or sauce. Baking can help retain the nutrients in the food, but it can also cause a loss of vitamins and minerals if the food is overcooked or if high heat is used.
When it comes to blood sugar, it's important to be mindful of the types of ingredients used in baked goods, such as using whole grain flours and natural sweeteners like fruit purees. Additionally, when cooking meat with dry heat in the oven, AGEs can form. These AGEs have been associated with insulin resistance and inflammation.
Microwaving is a convenient cooking method that can help to preserve the nutritional value of our food. This method uses minimal exposure to heat and has been shown to allow many foods to retain a large amount of their nutritional value. Spinach, carrots, sweet potatoes, and broccoli all retained over 90% of their vitamin C. Some of the nutrient preservation depends upon the vegetables cooked and the cooking process. For example, microwaving caused the greatest loss of vitamin K in crown daisies and mallow, but the least loss of vitamin K in spinach and chard.
Microwaving can be a great way to reheat starchy carbohydrates that have been cooked and allowed to cool. In the “cooling” section above we discussed how starchy, glucose-spiking carbohydrates can be converted to resistant starches and are digested like fiber (which does not spike blood glucose levels). Who knew that microwaving leftovers can be convenient and help to stabilize blood sugar levels?
Points to Stew Over
The cooking method we use can have a significant impact on the nutritional value of the food and the resulting effect on blood sugar levels. When seeking to preserve the nutritional value of food (especially water-soluble vitamins), grilling is the best option. Other cooking options include, in order of best option to least nutrient-preserving method: baking, microwaving, steaming, and boiling (use the cooking water as a base to improve nutrient retention).
If reducing inflammation, mitigating insulin resistance, and stabilizing blood sugar are your goals, then try cooking, cooling, and reheating your starches (like reheating leftover pasta) to create a resistant starch. Steaming, boiling, and microwaving our food are also great options to optimize our metabolic health. When cooking meat, dry-heat cooking like grilling, frying, or baking can cause the production of advanced glycation end products and should be minimized. Try sticking to vegetables and plant products when grilling, frying, or baking since plants have fewer AGEs.
By considering the cooking method used when preparing our meals, we can choose techniques that retain the maximum amount of nutrients while minimizing the risk of harmful compounds. In this way, we can make cooking decisions that support our health goals.
Author: Dr. Colleen Gulick