When you hear the term “low-carb diet,” what name comes to mind?
Most people would say Dr. Atkins, the cardiologist who created the Atkins Diet and wrote several international bestsellers, beginning with “Dr. Atkins’ Diet Revolution” in 1972.
However, low-carb diets have actually been around for over 150 years.
In fact, the popular “Banting” weight loss diet was named after William Banting, an obese man who lost more than 50 pounds in the mid-1800s by following a low-carb diet. What’s more, he maintained his new weight by continuing to eat the same way for the rest of his life.
In addition to helping people lose weight, very-low-carb diets were used for diabetes management back in the early 1900s.
Low-Carb diets in the pre-insulin era
Before insulin was discovered, a diagnosis of diabetes was considered a death sentence for people with the form known today as type 1. Without any insulin, their bodies were unable to properly absorb nutrients and maintain normal blood sugar levels, which caused severe weight loss, malnutrition and organ damage that typically led to death within months.
In addition, many individuals with less severe diabetes (today’s type 2) were frequently admitted to the hospital with infections related to uncontrolled blood
sugar. Poor blood sugar control also placed them at high risk for heart attack, stroke and other diabetes-related conditions.
Diabetes specialists Dr. Allan and Dr. Joslin recommended a diet very low in carbs and calories and very high in fat, alternating with periods of fasting, for people with diabetes. This “starvation diet” helped control blood sugars in people with type 1 diabetes and allowed them to live longer. Unfortunately, these patients still lost weight, experienced severe fatigue and had an overall poor quality of life (104).
However, some patients with type 2 diabetes were prescribed a high-fat diet providing adequate calories and less than 20 grams of carbs per day (105).
Diabetic Cookery: Recipes and Menus was a popular cookbook written by Rebecca Oppenheimer in 1917. Her meal-planning guidance includes recipes served to patients at diabetes treatment centers where she worked.
Foods allowed on the diet included:
Meat: beef, pork, lamb, poultry, or fish with cream sauce
Eggs and Dairy: cheese soufflé, egg pudding with ham and chives
Vegetables: greens with sour cream dressing, baked cauliflower with butter and cheese, creamed mushrooms
Fruit: (only on MD’s orders) small sour apple, 1/2 cup berries
Dessert: coffee cake made with almond flour, Bavarian cream, chocolate mousse (all sweetened with sugar-free sweetener)
Although restricting carbs could only go so far in helping type 1’s manage blood sugar without insulin, many people with type 2 diabetes thrived on a
Indeed, most type 2’s who strictly followed the diet were able to maintain stable blood sugar control and live in good health for years on a low-carb diet without any diabetes medication.
Dietary recommendations for diabetes following the discovery of insulin
Things changed, however, once injectable insulin was discovered by Dr. Best and Dr. Banting (a distant relative of William Banting) in 1921.
This was one of the most important advances in medicine and undeniably a lifesaver for people with type 1 diabetes, who could now eat normal amounts of food and absorb nutrients, prevent blood sugar from rising to dangerous levels and have a shot at a normal life.
Insulin — and later, diabetes medications — also allowed people with type 2 diabetes to consume high-carb foods. As a result, very-low-carb diets fell out of favor, although diabetic diet recommendations remained lower than for the general public.
For instance, up until the mid-1900s, diets prescribed for people with diabetes typically provided 20-30% of calories as carbs, or 100-150 grams on a
2000-calorie diet (106).
However, in the early 1950s, due in part to concerns that high-fat diets might cause heart disease, the American Diabetes Association (ADA) and other organizations changed course regarding their dietary recommendations.
Between the 1950s and 1986, daily carbohydrate recommendations gradually increased, reaching as high as 60% of calories in 1986 (106).
A 2000-calorie diet providing 60% of calories from carbs would mean 300 grams of carbs per day.
In addition, the ADA warned that all diets should provide a minimum of 130 grams of carb daily in order to provide adequate fuel for the brain (107).
The ADA’s current position on low-carb diets for diabetes
The tide seems to be turning again, however.
In 2013, after reviewing dozens of older and recent studies on low-carb diets, researchers at the ADA published nutrition guidelines stating that they are one of several eating patterns that may be used for diabetes management (41).
What’s more, the statement that 130 grams of carb per day is necessary to protect brain function no longer appears in any of the ADA’s diabetes management guidelines.
These changes are important, because they put to rest the idea that a healthy diabetic diet must provide a certain percentage of calories from carbs.
In the next section, you’ll learn how low-carb diets can significantly reduce blood sugar levels due to the unique changes they produce in your body — and why you don’t need to consume anywhere near 130 grams of carb daily to keep your brain healthy.
Low-carb diets are ideal for people with diabetes and prediabetes.
They’re undeniably effective at reducing blood sugar and insulin levels due to their unique mechanism.
Typical diabetic diets are centered around moderate to high carb intake with deliberate restriction of calories, fat or both.
By contrast, low-carb diets help regulate blood sugar by changing your body’s primary fuel source from sugar to fat without consciously restricting calories, fat or protein.
Instead of eating a bunch of carbs, experiencing a blood sugar spike and then using drugs to try to force your blood sugar back down, you simply stop eating so much sugar.
You cut the blood glucose at the source, instead of letting it go up and then trying to minimize the damage afterwards — a proactive rather than a reactive approach.
Metabolic changes that occur during carb restriction
Normally, your body’s cells use sugar (glucose) for energy. However, this isn’t the only source of fuel they can use.
Many cells can also use fat or ketone bodies (ketones), compounds produced by your liver from the fat you eat and the breakdown of stored body fat.
When you eat fewer than 50 grams of digestible carbs per day, your blood sugar and insulin levels go down significantly.
This decrease in blood sugar and insulin stimulates your liver to step up its production of ketones (108).
Importantly, ketones aren’t a harmful or abnormal substance produced by the body.
In fact, your body makes ketones whenever you don’t eat for many hours, such as after a full night’s sleep. This ensures that your body has a continued energy source even when carb intake is very low.
Many cells can use ketones or fatty acids just as effectively as glucose. However, certain cells and organs can only use glucose. These include red blood cells and portions of the brain, eye and kidney.
In fact, one of the arguments frequently used against low-carb diets is that the brain needs 130 grams of carb per day to function properly.
However, during starvation conditions or extremely low carb intakes, ketones can provide up to 70% of the brain’s energy needs (109).
Moreover, a report by the US Institute of Medicine’s Food and Nutrition Board states:
“The lower limit of dietary carbohydrates compatible with life apparently is zero, provided that adequate amounts of protein and fat are consumed.”
What about the cells that can only use glucose?
Fortunately, you don’t need to starve or follow a zero-carb diet to control your blood sugar.
Ideally, you should consume at least 20 grams of healthy carbs daily in order to provide fiber, phytochemicals, vitamins and minerals.
In fact, you may be able to consume twice this amount, or even more, and still maintain healthy blood sugar levels.
The optimal amount for you will be based on your own personal carb tolerance, which you’ll determine a little later in the course.
The carbs you eat will provide a small amount of sugar for any cells that can’t use ketones for energy.
However, in order to make sure there is always a steady supply of sugar for these cells, your body has a system in place to provide as much as it needs.
Like ketosis, this process takes place mainly in the liver.
Gluconeogenesis is the process of making glucose out of non-carb sources like amino acids from protein and glycerol from fat. As you may recall, this process was briefly discussed in Section 2.3 on protein metabolism.
Indeed, even if no carb at all is consumed, it’s estimated that up to 200 grams of glucose per day can be created via gluconeogenesis, if needed (108).
Blood sugar and insulin response to low-carb diets
Keeping carb intake low can have profound effects on your blood sugar and insulin levels.
When few carbs are eaten, blood sugar rises very little after eating before returning to its previous level within an hour or so. Therefore, blood sugar levels stay within a healthy narrow range throughout the day.
What’s more, your blood sugar improves not only because there is less glucose coming into the body, but also because insulin sensitivity increases as well. This can help lower your fasting blood sugar (110).
There are many high-quality studies showing that carb restriction can lead to dramatic decreases in blood sugar and insulin levels and improved insulin sensitivity, which you’ll learn all about in the next section.
Switching to a low-carb diet can significantly improve your diabetes control.
Even if this way of eating offered no other health benefits, these effects alone would be enough to recommend it for everyone with diabetes or prediabetes.
But low-carb diets can have all kinds of other impressive effects on health.
Indeed, depending where you fall on the prediabetes-diabetes spectrum and how you personally respond to the diet, the changes you experience may be nothing short of spectacular.
Here are 9 diabetes-related benefits of a low-carb lifestyle.
Well-controlled blood sugar around the clock
A low-carb way of eating can help keep your blood sugar in the healthy range all day and throughout the night.
Studies in people with diabetes have shown that both fasting blood sugar and postprandial blood sugar (blood sugar after meals) improve more on low-carb diets than standard low-calorie diabetic diets (80, 111, 112, 113, 114).
Alt this point, researchers aren’t able to measure people’s blood sugar levels every minute during the course of a study. However, they do measure hemoglobin A1c, which reflects a 3-month average of your blood sugar at all time points.
In a controlled study, people with type 2 diabetes or prediabetes followed either a low-carb, non-calorie-restricted diet with less than 50 grams of digestible carbs per day or a moderate-carb, calorie-restricted diet for 3 months (80).
At the end of the study, average fasting blood sugar had decreased by 11% in the low-carb group but only 1% in the moderate-carb group.
This means that the low-carb diet was more than 10 times as effective at lowering fasting blood sugar.
In addition, 56% of people who ate low-carb decreased their A1c by at least 0.5%
— more than twice as many as those on the moderate-carb eating plan.
As you can see in the graphs below, everyone in the low-carb group lowered their A1c, whereas some people in the moderate-carb group actually had an increase.
(Photo source: https://www.ncbi.nlm.nih.gov/pubmed/24717684)
Reduction or elimination of diabetes medication
One of your goals may be to discontinue using insulin or diabetes medicine. Although not everyone with type 2 diabetes will be able to manage their blood sugar with diet changes alone, carb restriction can give you the best shot at achieving this.
Indeed, many people with type 2 find that eating a very-low-carb diet allows them to maintain healthy blood sugar levels without taking any medication.
According to Dr. Eric Westman, who has treated many people with diabetes using a low-carb approach, he needs to reduce their insulin dosage by 50% on the first day (105).
Moreover, even if you aren’t able to completely discontinue insulin or other diabetes meds, there’s plenty of evidence suggesting you’ll likely need far less on a carb-restricted diet (60, 80, 112, 115, 116).
In one study where type 2 diabetics consumed a very-low-carb diet, 95.2% had managed to reduce or eliminate their glucose-lowering medication within 6 months (112).
In another, 21 overweight people with type 2 diabetes followed a diet providing about 20 grams of carb daily for 16 weeks. By the end of the study, 10 people had significantly decreased their diabetes medication and/or insulin dosage, and 7 people were able to discontinue diabetes drugs altogether (60).
One of the men in this second study decreased his daily insulin dosage from 100 units to just 8 units per day. Due to eating a low-carb diet, he no longer required mealtime insulin at all. Instead, he took only a small amount of background insulin to ensure his blood sugar remained in his target range at all times (60).
Fewer low blood sugar episodes if taking insulin
Despite what well-meaning people may have told you, following a low-carb diet doesn’t increase your risk of low blood sugar if you take insulin.
In fact, it’s actually safer than consuming a high-carb diet because you’ll be using significantly less insulin.
Dr. Richard K. Bernstein, a diabetes specialist who has lived with type 1 diabetes for more than 60 years, calls this The Law of Small Numbers.
The basic idea is that eating small amounts of carbs and taking small amounts of insulin leads to more predictable blood sugar response and less chance of overestimating the amount of insulin you need. Taking too much insulin can cause hypoglycemia, or dangerously low blood sugar.
At this time, there are few, if any, studies in people with type 2 diabetes that have looked at whether carb restriction increases or decreases risk of low blood sugar episodes.
However, because insulin dosage is dramatically reduced on a low-carb diet — if not discontinued altogether — the likelihood of hypoglycemia would be reduced as well.
A group of Swedish researchers did explore whether low-carb diets reduce risk of low blood sugar in people with type 1 diabetes, who must take insulin every day regardless of the diet they follow.
In this 12-month study, adults with type 1 diabetes who consumed 70-90 grams of carbs per day were able to reduce their daily insulin needs substantially. As a
result, they had 82% fewer episodes of hypoglycemia than before they started the diet (117).
Lower insulin levels and greater insulin sensitivity
Low-carb diets can help reduce your blood insulin levels. This makes sense, because when you consume fewer carbs, you need less insulin to maintain blood sugar within a healthy narrow range.
In some cases, these changes can be quick and dramatic.
In a small study of 10 obese adults with type 2 diabetes who followed a low-carb, high-protein diet, insulin sensitivity improved by an impressive 75% within only 2 weeks (111).
What’s more, you may achieve similarly impressive results if you have prediabetes.
In a 12-week controlled study of 40 adults with prediabetes, half of the people ate a diet providing about 45 grams of carb per day, and the remainder ate a low-fat diet providing about 210 grams of carb per day.
The low-carb group achieved a 50% decrease in blood insulin and a 55% increase in insulin sensitivity, in addition to several other metabolic improvements. By contrast, the low-fat group experienced only small improvements overall (37).
(Photo source: citeseerx.ist.psu.edu)
Prevent progression from prediabetes to diabetes
Although it’s true that not everyone who has prediabetes will eventually become diabetic, it’s impossible to know who will be spared. If you have prediabetes, your best course of action is to follow the same low-carb way of eating that works so well for people with diabetes. It can only benefit your health.
What’s more, in some cases, you may actually be able to reverse the process so that you are no longer even considered prediabetic.
In one study, 22 obese prediabetic adults followed a Mediterranean diet containing 30 grams of carbs per day. After 12 weeks, their fasting blood sugar
had dropped from an average of 119 mg/dL (6.6 mmol/L) to an average of 92 mg/dL (5.1 mmol/L), which is considered normal blood sugar (79).
Reduced risk of complications related to high blood sugar
Uncontrolled blood sugar can cause long-term organ damage that dramatically reduces your quality of life.
Diseases linked to poor blood sugar control include:
Chronic kidney disease (CKD)
Peripheral artery disease (PAD)
Cataracts, glaucoma and other eye disorders
Large, decades-long studies in people with type 1 and type 2 diabetes have found that the risk of developing complications can be minimized or even prevented by keeping blood sugar well controlled at all times (119, 120).
Unfortunately, trying to accomplish this with large doses of insulin or drugs may actually end up increasing your odds of developing serious health problems that may even lead to death (121).
On the other hand, following a low-carb diet can help keep your blood sugar under excellent control in a safe and sustainable way long-term.
Improved heart and metabolic health
A well-balanced low-carb diet may help protect your heart.
This is good news, since having diabetes or prediabetes is a major risk factor for heart attacks and strokes. In fact, researchers estimate that at least two thirds of all people with heart disease have diabetes or prediabetes (122).
It’s clear that eating too many carbs can have disastrous consequences on metabolic health.
Elevated blood sugar due to high carb intake has been linked to heart disease, increased insulin resistance and obesity (123).
Low-carb diets not only help keep blood sugar and insulin levels under control, but they’ve also been shown to improve heart health markers, including:
Indeed, a detailed analysis of 17 controlled studies of more than 1700 people found that low-carb diets led to greater reduction in heart disease risk factors when compared to low-fat diets (128).
Most people with prediabetes or type 2 diabetes tend to have low HDL levels and high triglyceride levels — the exact opposite of what is considered healthy.
In one study, 15 overweight men consumed a low-fat diet and a very-low-carb diet for 6 weeks each. After the very-low-carb diet, their fasting triglycerides decreased by an impressive 44%, whereas the low-fat diet had no effect on triglycerides. In addition, their triglycerides went up significantly less after meals, and their ratio of triglycerides to HDL decreased (124).
Significant reduction in weight and belly fat
If you have diabetes or prediabetes and want to lose weight, a low-carb diet is your best bet by far.
In addition, they seem to be especially effective at reducing belly fat, also known as trunk fat or visceral fat, the type linked to insulin resistance, heart disease risk and other health problems (79, 118, 133, 134).
In one study, 15 overweight or obese men and women followed a very-low-carb or low-fat diet for 30 to 50 days. At the end of the low-carb-diet period, there was greater loss of fat from all areas of the body, including belly fat, than after the low-fat diet (134).
(Photo source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC53827…)
Therefore, you naturally reduce the amount of calories you consume without feeling hungry.
In a small study, when 10 obese diabetic adults followed a low-carb diet for 2 weeks, their average daily calorie intake dropped by more than 1000 calories without deliberately limiting how much they ate (111).
Poor diabetes control leads to premature aging that can both shorten your life and decrease its quality.
It’s estimated that more than 3 million people die annually because of diabetes or its complications, and researchers suggest that making diet and lifestyle changes could go a long way toward reducing these numbers (137).
As discussed previously, the hemoglobin A1c value reflects your blood sugar average over about a 3-month period. It actually measures the amount of sugar that’s attached to your red blood cells. The more sugar you have in your blood, the higher your A1c value will be.
One study found that over a 10-year period, having a high hemoglobin A1c — or fluctuating between high and low values — increased risk of diabetes complications by up to 45% and death by up to 27% (140).
Achieving and maintaining good blood sugar control by making low-carb a permanent lifestyle change can help you live a longer, higher-quality life.
As you’ve learned, there are many benefits of following a carb-restricted diet to control blood sugar and improve your health.
After reviewing a few Frequently Asked Questions and Resources, you’ll be ready to move on to Part 4, where you’ll learn all about low-carb living, including how to customize your own plan to make it a perfect fit for you.
Here are a few books that cover the history and science behind low carb diets for diabetes:
The World Turned Upside Down: The Second Low Carbohydrate Revolution by Richard D. Feinman, PhD