Figuring out how many carbs to eat when you have diabetes can
Meal plans created by the American Diabetes Association (ADA) provide
about 45% of calories from carbs. This includes 45–60 grams per
meal and 10–25 grams per snack, totaling about 135–230 grams of
carbs per day.
However, a growing number of experts believe people with
diabetes should be eating far fewer carbs than this. In fact,
many recommend fewer carbs per day than what the ADA
allows per meal.
This article takes a look at the research supporting low-carb
diets for diabetics and provides guidance for determining
optimal carb intake.
What Are Diabetes and Prediabetes?
Glucose, or blood sugar, is the main source of fuel for your
In people with diabetes, the body’s ability to process and use
blood sugar is impaired.
Although there are several types of diabetes, the two most
common forms are type 1 and type 2 diabetes.
Type 1 Diabetes
In type 1 diabetes, the pancreas is unable to produce insulin,
a hormone that allows sugar from the bloodstream to enter the
body’s cells. Instead, insulin must be injected to ensure that
sugar enters cells.
Type 1 diabetes develops because of an autoimmune process in
which the body attacks its own insulin-producing cells, which
are called beta cells. This disease is usually diagnosed in
children, but it can start at any age, even in late adulthood
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Type 2 Diabetes
Type 2 diabetes is more common, accounting for about 90% of
people with diabetes. Like type 1 diabetes, it can develop in
both adults and children. However, it isn’t as common in
children and typically occurs in people who are overweight or
In this form of the disease, either the pancreas does not
produce enough insulin or the body’s cells are
resistant to insulin’s effects. Therefore, too much sugar
stays in the bloodstream.
Over time, the beta cells of the pancreas can wear out as a
result of pumping out more and more insulin in an attempt to
lower blood sugar. They can also become damaged from high
levels of sugar in the blood (2).
Diabetes can be diagnosed by an elevated fasting blood sugar
level or an elevated HbA1c level, which reflects blood sugar control
over a period of two to three months.
Diabetes is diagnosed by a fasting blood sugar of at least 126
mg/dL (7 mmol/L) or an HbA1c of at least 6.5% (3).
Before type 2 diabetes occurs, blood sugar levels are elevated
but not high enough to be diagnosed as diabetes. This stage is
known as prediabetes.
Prediabetes is diagnosed by a blood sugar level between 100–125
mg/dL (5.6–6.9 mmol/L) or an HbA1c between 5.7–6.4% (3).
While not everyone with prediabetes goes on to develop type 2
diabetes, it’s estimated that approximately 70% will eventually
become diabetic (4).
What’s more, even if prediabetes never progresses to diabetes,
people with this condition may still be at an increased risk of
heart disease, kidney disease and other complications related
to high blood sugar levels (4).
Bottom Line: Type 1 diabetes is due to the
destruction of pancreatic beta cells, while type 2 diabetes
occurs when cells are resistant to insulin or the pancreas
doesn’t make enough. Prediabetes often progresses to
How Does Food Affect Blood Sugar Levels?
Blood sugar levels are affected by many things, including
exercise, stress and illness.
However, one of the major factors affecting your blood sugar is
the type and amount of food you consume.
Of the three macronutrients — carbs, protein and fat —
carbs have the greatest effect on blood sugar by far.
This is because when your body digests carbs, they are broken
down into sugar, which enters your bloodstream.
This occurs with all carb-containing foods, such as refined
carb sources like chips and cookies, as well as healthy types
like fruits and vegetables.
However, whole foods contain fiber.
Unlike starch and sugar, naturally occurring fiber in food does
not raise blood sugar levels.
When diabetics eat foods high in digestible carbs, their blood
sugar can rise to very high levels. Eating large portions of
these foods typically requires high doses of insulin or
diabetes medication to control blood sugar.
Because they are unable to produce insulin, people with type 1
diabetes need to inject insulin several times a day, regardless
of what they eat. However, eating fewer carbs can significantly
reduce their mealtime insulin dosage.
Bottom Line: Your body breaks down carbs
into sugar, which enters the bloodstream. People with
diabetes who eat a lot of carbs require insulin or medication
to keep their blood sugar from rising too much.
Research on Carb Restriction for Diabetes
There are many studies supporting the use of carb restriction
Very Low-Carb, Ketogenic Diets
Very low-carb diets typically induce mild to moderate ketosis,
a state in which your body uses ketones and fat, rather than
sugar, as its main energy sources.
Ketosis usually occurs at daily intakes of less than 50 grams
of total carbs, or 30 grams of digestible carbs (total carbs
minus fiber). This would be no more than 10% of calories on a
Several studies have shown that restricting carb intake to
20–50 grams of carbs per day can significantly reduce blood
sugar levels, promote weight loss and improve heart health
markers in people with diabetes (6, 7, 8, 9, 10, 11, 12, 13, 14, 15).
In addition, these improvements often occur very quickly.
For instance, in a study of obese people with diabetes,
limiting carbs to 21 grams per day led to a spontaneous
decrease in calorie intake, lower blood sugar levels and a 75%
increase in insulin sensitivity in two weeks (14).
In a small, three-month study, people were randomized to
consume a calorie-restricted, low-fat diet or a low-carb diet
containing up to 50 grams of carbs per day.
The low-carb group had an average decrease in HbA1c of 0.6% and
lost over twice as much weight as the low-fat group. Also, 44%
of the low-carb group discontinued at least one diabetes
medication, compared to 11% of the low-fat group (15).
In a small, 12-week study of obese, prediabetic men who
followed a Mediterranean diet limited to 30 grams of carbs per
day, fasting blood sugar dropped to 90 mg/dL (5 mmol/L), on
average, which is well within the normal range (17).
In addition, the men lost an impressive 32 pounds (14.5 kg) and
experienced significant reductions in triglycerides,
cholesterol and blood pressure, among other beneficial health
Importantly, these men no longer met the criteria for metabolic
syndrome due to reductions in blood sugar, weight and other
Although concerns have been raised that higher protein
intake on low-carb diets may lead to kidney problems, a
recent 12-month study found that very low carb intake did not
increase the risk of kidney disease (18).
Bottom Line: Many studies have shown
restricting carbs to 20–50 grams, or less than 10% of
calories, per day may lower blood sugar, promote weight loss
and improve health markers in people with diabetes and
There is currently no agreement on how many carbs a
low-carb diet contains.
However, for purposes of this article, the term “low-carb” will
refer to diets containing 50–100 grams of carbs, or 10–20% of
calories, per day.
Although there are very few studies on carb restriction for
type 1 diabetics, most that exist have used carb intakes in the
low-carb range. In each case, impressive results have been
reported (19, 20, 21).
In a long-term study of people with type 1 diabetes who were
advised to restrict carbs to 70 grams per day, those who
complied reduced their A1c from 7.7% to 6.4%, on average.
What’s more, their A1c levels remained the same four years
A 1.3% reduction in HbA1c is a significant change to maintain
over several years, particularly in those with type 1 diabetes.
One of the biggest concerns for people with type 1 diabetes is
hypoglycemia, or blood sugar that drops to dangerously low
In a 12-month study, adults with type 1 diabetes who restricted
daily carb intake to less than 90 grams had 82% fewer episodes
of low blood sugar than before they started the diet (21).
In a small, five-week study, men with type 2 diabetes who
consumed a high-protein, high-fiber diet providing 20% of
calories from carbs per day experienced a 29% reduction in
fasting blood sugar, on average (23).
Bottom Line: Research suggests a daily carb
intake of 50–100 grams, or 10–20% of calories, may lower
blood sugar levels in people with diabetes. It may also help
reduce episodes of low blood sugar in people who take
Moderate, Low-Carb Diets
As with “low-carb” diets, there is no formal definition for
“moderate, low-carb diets.” In this article, “moderate
low-carb” will refer to diets providing 100–150 grams of
digestible carbs, or 20–35% of calories, per day.
In a 12-month study of 259 people with type 2 diabetes, those
who followed a Mediterranean
diet providing 35% or fewer calories from carbs experienced
a significant reduction in HbA1c, from 8.3% to 6.3%, on average
Bottom Line: A few studies have found that
diets providing 100–150 grams of carbs, or 20–35% of
calories, per day may lower blood sugar levels in people with
How Low Should You Go?
Research has confirmed that many levels of carb restriction
blood sugar levels.
Since carbs raise blood sugar, reducing them to any extent can
help control how much your blood sugar rises after eating.
For instance, if you’re currently consuming about 250 grams of
carbs daily, reducing your intake to 130 grams should result in
significantly lower blood sugar after meals, as the few,
moderate, low-carb studies that are available have shown.
However, most studies have looked at blood sugar response in
people with diabetes who consume 20–50 grams of carbs per day.
This level appears to produce the most dramatic results,
including blood sugar improvement that reduces or even
eliminates the need for insulin or diabetes medication.
Bottom Line: Studies have shown that a daily
carb intake between 20–150 grams, or 5–35% of calories, may
effectively manage diabetes and prediabetes. Very low-carb
diets may have the greatest effect.
High-Carb Foods to Limit or Avoid
There are many tasty, nutritious, low-carb foods that do not
raise blood sugar levels very much.
These can be enjoyed in moderate to liberal amounts on low-carb
However, there are certain foods that should be limited or
avoided because of their high carb content:
- Breads, muffins, rolls and bagels
- Pasta, rice, corn and other grains
- Potatoes, sweet potatoes/yams and taro
- Legumes like peas, beans and lentils (except green beans,
snow peas and peanuts)
- Milk and sweetened yogurt
- Most fruit, except for berries
- Cake, cookies, pie, ice cream and other sweets
- Snack foods like pretzels, chips and popcorn
- Juice, soda, sweetened iced tea and other sugar-sweetened
Keep in mind that not all of these foods are unhealthy. For
fruits and legumes
can be highly nutritious. However, they can be problematic for
diabetics who are trying to manage their blood sugar levels by
eating fewer carbs.
On the other hand, you can eat plenty of low-carb vegetables,
nuts, seeds, avocados, meat, fish, eggs, full-fat dairy and
See a longer list of healthy, low-carb foods in this
Bottom Line: Although many delicious foods
can be included on a low-carb diet, those that are high in
carbs should be limited or avoided altogether.
Are Low-Carb Diets Always Best for Diabetes?
Low-carb diets have consistently been shown to lower blood
sugar and improve other health markers in people with diabetes.
However, certain higher-carb diets have also been credited with
similar beneficial health effects.
In a 12-week study, a brown rice-based vegan diet containing
268 grams of total carbs (72% of calories) lowered people’s
HbA1c more than the standard Korean Diabetes Association diet
containing 249 grams of total carbs (64% of calories) (30).
An analysis of four studies found that people with type 2
diabetes who followed a low-fat, macrobiotic diet containing
about 70% of calories from carbs achieved significant
reductions in blood sugar and other health markers (31).
However, it’s important to note that these diets weren’t
directly compared to low-carb diets, but rather to standard,
diets often used for diabetes management.
In addition, there aren’t as many studies on these diets as
there are on low-carb diets. While they may be effective for
certain people, more research is needed to confirm these
Bottom Line: Studies suggest that certain
higher-carb diets may be effective for diabetes management.
However, research comparing these diets to low-carb diets is
How to Determine Optimal Carb Intake
Although studies have shown that many different levels of carb
intake may help control blood sugar, the optimal amount varies
It is worth repeating that diets containing 20–50 grams of
carbs per day have been studied the most and typically produce
the most dramatic results in diabetics.
However, in addition to keeping blood sugar levels within a
healthy range, it’s important to eat the amount of carbs at
which you feel best, as well as that you can realistically
maintain in the long term.
Therefore, figuring out how many carbs to eat requires some
testing and evaluating to find out what works best for you.
To determine your ideal carb intake, measure your blood sugar
with a blood glucose meter before a meal and again one to two
hours after eating.
The maximum level your blood sugar should reach is 139 mg/dL (8
mmol/L) in order to prevent damage to blood vessels and nerves.
However, you may want to aim for an even lower upper limit.
To achieve your blood sugar goals, you may need to restrict
your carb intake to less than 10 grams, 15 grams or 25 grams
Also, you may find that your blood sugar rises more at certain
times of the day, so your upper carb limit may be lower for
breakfast than lunch or dinner.
In general, the fewer carbs you consume, the less your blood
sugar will rise and the less diabetes medication or insulin
you’ll require to stay within a healthy range.
If you take insulin or diabetes medication, it’s very important
to speak with your doctor or health care provider prior to
reducing your carb intake so that your dosage can be adjusted
to prevent low blood sugar.
Bottom Line: Determining the optimal carb
intake for diabetes management requires testing your blood
sugar and making adjustments as needed based on your
response, including how you feel.
Take Home Message
Based on the evidence to date, conventional recommendations
that diabetics should consume at least 45% of their daily
calories from carbs appear misguided.
Multiple studies have shown that a daily carb intake of 20–150
grams, or between 5–35% of calories, not only leads to better
blood sugar control but may also promote
weight loss and other health improvements.
Therefore, a carb-restricted approach may be your best bet to
keep your blood sugar within a healthy range.
However, even among people with diabetes, some individuals can
tolerate more carbs than others.
Testing your blood sugar and paying attention to how you feel
at different carb intakes can help you find your own personal
range for optimal diabetes control, energy levels and quality