How Protein, Fat, Carbs, and Fiber Affect Blood Sugar

Here’s what you need to know about these important nutrients—and the role they play in managing blood sugar and diabetes.
protein, fat, carbs and fiber

Article summary: Nutrients For Blood Sugar Control

When it comes to blood sugar and diabetes, there’s a lot of talk about limiting carbohydrates. And that makes sense—carbs are a major driver of your blood sugar levels, namely how fast glucose is absorbed into the blood. But you also need carbs to survive; they’re the body’s main source of fuel to power your muscles, your nervous system, your brain, the works. It’s the types of carbs you eat that become more important when you’re laser-focused on keeping blood sugar stable. 

That said, carbs aren’t the only nutrient that matters. Food also contains protein, fat, and a type of carb called fiber, all of which play a role in how your body regulates glucose. Sound overwhelming? It may seem like a lot to keep in mind at meal time, but once you understand these nutrients—and know what to aim for at every meal—you’ll be confident that you’re making wise choices and striking the right balance. Even better, you’ll feel the difference in your body when you’re fueling up on healthy foods. Here, we’ll break down the macronutrients to keep in mind when putting together a well-rounded, nutritious diet that helps to keep blood sugar in check.


What are carbohydrates?

Carbohydrates are naturally occurring sugars, starches, and fiber found in food. When you eat carbs, the sugars and starches get broken down into glucose which gets released into the bloodstream. Your body then taps the glucose for energy when you need it, and stores any excess glucose for energy later.

Wondering what happens to the fiber component of carbs? Hang on, we’ll get back to that. For now, let’s focus on starches and sugars. Carbs that are high in sugars and starches are—you guessed it—going to spike your blood sugar levels. Your refined and highly processed carbs, like white bread, pasta, white rice, cookies and cakes, all fall into this category because their sugars are easily digestible, so the body quickly turns them into glucose, which shoots right into the bloodstream. (See a more complete list of these speedy-sugar-delivery carbs below). 

Whole grains, on the other hand, are also loaded with carbs but they aren’t as refined as the processed kind. Your digestive system must work a little harder to break them down into glucose, which means they don’t cause blood sugar to rise as quickly. Bonus: they provide your body with other good-for-you vitamins and minerals (which have often been stripped out of processed foods).

How many carbs should you eat in a day? 

Low-carb and no-carb diets have been falling in and out of favor for decades. But one thing’s for sure: You need carbs for energy because they fuel your brain, muscles, and other vital organs. You can go very low carb, but you’ll need to make sure your body doesn’t miss out on important nutrients along the way. And because everyone’s biology and lifestyle is different, it’s impossible to give a simple one-size-fits-all answer on exactly how many carbs you should eat. The American Diabetes Association recommends that a fourth of your plate at each meal contain carbs to prevent blood sugar levels from spiking (more on that healthy-plate model in a bit), but you’ll still want to consult with a doctor or nutritionist to develop a personalized daily carb limit based on your health goals.

Good vs. Bad Carbs

The more sugary carbs you consume, the more insulin your body produces, whether you need it or not. This can lead to a condition called insulin resistance, in which your body’s cells stop responding effectively to insulin. When this happens, more glucose stays in your blood, causing your blood sugar levels to stay chronically high, which puts you at increased risk of developing prediabetes and diabetes. The bottom line: Steering clear of processed food loaded with added sugars is a very smart health move.


What is fiber?

Fiber is a type of carb. And, while yes, we just talked about steering clear of too many carbs, do your body a favor and make an exception for fiber-filled foods. Why? Because fiber is a type of carb that your body can’t digest. In other words, it can’t be broken down into sugar molecules, so it hasn’t been shown to have any negative effect on your blood sugar levels. (That’s why, when you’re reading food labels, you should subtract the fiber from the total carbs when calculating the amount of carbs you’re consuming that will actually affect your blood sugar level.) 

First, we should mention that there are two types of fiber:

  • Soluble fiber: This type of fiber, found in foods including many veggies, fruits, beans, and some nuts, dissolves in water and is the type most linked with leveling out blood sugar and lowering cholesterol.
  • Insoluble fiber: This type of fiber, found in a range of foods including whole grains and legumes, doesn’t dissolve in water and is the type that helps stave off constipation and aids in proper digestion by keeping foods moving smoothly through your system.

Fiber is an all-around winner in the nutrition department: Beyond stabilizing blood sugar, it helps reduce cholesterol and promote a healthy weight. A 2019 study of diabetes patients by researchers in India found that a high fiber diet can have a stunningly positive effect on health outcomes. Over the course of six months, study subjects consumed an average of 30g of fiber daily. By the end of the study, they reported a 28 percent reduction in fasting glucose. It also reduced their numbers across the board: cholesterol, triglycerides, and blood pressure all trended downward, too. “A high fiber diet is important in cases of diabetes and hypertension to prevent future cardiovascular disease,” said study author Rohit Kapoor, MD, medical director of Care Well Heart and Super Specialty Hospital, in a review by the American College of Cardiology. Other studies have shown that when you consume a meal high in fiber, your blood sugar won’t spike as much in the hours after you eat.

The reasons are complex, explains Maziyar Saberi, PhD, is a systems physiologist and Chief Scientific Officer of January AI. “Some fibers dampen glucose spikes by physically interacting with the foods we eat, slowing down digestion and therefore, slowing down the amount of glucose released into circulation. The same process holds true for reducing cholesterol levels. Other fibers interact with the intestinal microbiome to increase the production of a number of key bioactives. Those, in turn, help to steady blood glucose, regulate hunger, and reduce inflammation.”

How much fiber do you need?

Most adults don’t consume even close to the recommended amount of fiber each day. According to the USDA’s 2020 Dietary Guidelines for Americans, healthy adult women should aim for about 28 grams daily while men should shoot for about 34. 

The American Diabetes Association says this is a good guideline for those with diabetes or prediabetes, but you may want to be an overachiever when it comes to fiber. Take a small study in the New England Journal of Medicine, for instance, which found that people who consumed more than 50 grams per day, specifically soluble fiber, were better able to control their glucose levels compared to those who only consumed 24 grams. Plus, studies have shown that low fiber diets significantly increased the risk of type 2 diabetes because low-fiber foods tend to spike blood sugar more. 

What are good sources of fiber?

  • Vegetables, including: acorn and butternut squash; collard greens; kale; broccoli; carrots; spinach; Brussels sprouts; green beans; sweet potatoes; asparagus
  • Fruits, including: avocado (yes, it’s a fruit, and it tops the list for fiber); raspberries and blackberries; pears; kiwi; pomegranate; citrus, such as oranges and tangerines
  • Beans and legumes, including: chickpeas, lentils; green peas; edamame; many kinds of beans, such as kidney, black, pinto and navy.
  • Whole grains, including: bulgur; kamut; pearl barley; quinoa; buckwheat


What is protein? 

Protein plays a key role in building muscle mass and is vital for every body part and tissue. During the digestive process, the protein in your food gets broken down into amino acids. These amino acids are then absorbed by the small intestine where they enter the bloodstream and get to work repairing cells and building strong muscles.

Protein doesn’t have much effect when it comes to glucose levels, but you still want to remain mindful of how much of this macronutrient you’re consuming, and where it comes from (salmon is going to be better for you than steak, for example). Regarding protein and diabetes, one 2016 Harvard study found that people with prediabetes who consumed a diet high in animal protein had a 13 percent higher risk of developing type 2 diabetes compared to those who consumed the least amount of animal protein. Vegetable sources of protein, on the other hand, gave them a bit of protection from the disease.

How much protein do you need? 

According to the USDA’s Dietary Guidelines for Americans, most healthy adults should aim to have 10 to 35 percent of daily calories come from protein. That’s about 46 grams for women and up to 56 grams for men. Talk with your doctor or a nutritionist about what’s the best daily protein target for your health goals and activity level. 

Good protein sources

When picking your proteins, focus on foods that are overall healthy and low in fat and carbs. Some high-protein foods can also be high in saturated fat (your average bacon cheeseburger, for instance) which isn’t helpful because saturated fat can increase your risk of heart disease and stroke. Instead, opt for lean protein that allows you to keep blood sugar levels stable, like these options:

7 Healthy Sources of Protein:

  • Seafood, including: salmon; trout, mackerel; herring; sardines; shrimp; clams; mussels; oysters; crab; lobster
  • Poultry, including: chicken and turkey
  • Eggs
  • Tofu
  • Nuts and seeds, including: quinoa; chia seeds; almonds; pistachios; hazelnuts
  • Beans and legumes, including: chickpeas; kidney beans; green peas; edamame; lentils; and peanuts
  • Veggies, including: spinach; kale; broccoli; cauliflower; mushrooms; artichokes


What is fat, and can it be healthy? 

For years low-fat diets were all the rage because they were thought to improve health. Now we know that all fats aren’t created evil, or equal. Saturated fats—the kind that increase your risk for heart disease and stroke—are the ones you really want to limit. But mono-and poly-unsaturated fats—the good kind of fat found in healthy nuts and fish—can actually have a protective effect when consumed in moderation (they’ve been shown to help lower cholesterol levels). 

When it comes to blood sugar, fatty foods aren’t going to spike your levels much at all. But it’s those saturated fats you still have to worry about.Many studies, including one published in the journal Diabetes Care by researchers at the University of Colorado Health Sciences Center, have shown that a high-fat diet, especially one high in saturated fats, can increase your risk of developing type 2 diabetes while also putting you at greater risk for heart disease. And because we know obesity is a risk factor for type 2, you want to avoid packing on the pounds. Limiting saturated fats can help with that, too.

How much fat do you need?

So, while too much of any kind of fat is problematic—fats shouldn’t exceed about 35 percent of your daily calorie intake—the type of fat you consume truly does matter. As with protein, check with your doctor to make sure you’re hitting a target that’s most in line with your health goals. (For people managing diabetes that could be less than 35 percent of total calories.) 

Sources of Good Fats (mono- and poly-unsaturated fats)

  • Oils, including: olive and canola oil
  • Seeds and nuts, including: almonds; flaxseeds; cashews
  • Fish, including: salmon; mackerel; herring; sardines; trout
  • Avocado

Sources of Unhealthy Fats (saturated and trans fats)

  • Fatty meats, including: bacon; sausage; hot dogs
  • Dairy, including: cheese; butter; margarine
  • Most fast foods, including: burgers; fried foods; biscuits; donuts and pastries

Putting it All Together

Balancing all the different nutrients in your diet can easily make your head spin, especially when you’re trying to keep your calories in check, too. We know, it’s a lot to manage. But there are some simple strategies to help you get a grip on what you should eat. Try aiming for overall benchmarks for yourself by setting goals at every meal (use our plate model below). Then, create a running list of foods and recipes that you can pull from as you plan what to put on your plate. It’ll get easier when you have a line-up of foods you enjoy that also fit both your nutrient and calorie budgets, so you don’t have to run the numbers at every meal. You can think of it as “automating” certain meals: Maybe you alternate a few go-to breakfasts and lunches that help you get in lots of fiber and enough protein, with a little healthy fat thrown in. (And yes, switch them up when you get bored—because eating should be fun as well as fuel.) That leaves dinner a little more open and interesting. You can build out a recipe collection you like, constantly adding to it so you have plenty of options that deliver good nutrients, plus deliciousness. 

To get you started, consider splitting up your plate like this:

  • ½: non starchy vegetables (like roasted cauliflower or steamed broccoli)
  • ¼: protein (aim for sources high in good fats, like salmon, lean meat, or tofu)
  • ¼: carbs (focus on fiber!)

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