Nutrition and Diabetes – Carbs are the WORST

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Carbohydrates, fat and protein are the three macronutrients found in the food you eat. Of these, carbohydrates (carbs) have the greatest impact on your blood sugar by far, especially if you have prediabetes or diabetes.

The two main categories of carbs responsible for raising your blood sugar are starches and sugars:

Starches: Long chains of sugar (glucose) units linked together. Examples of high-starch foods include potatoes, rice and bread.

Sugars: Single sugar units (monosaccharides) or two sugar units linked together (disaccharides). Foods rich in natural sugars include fruit and milk, whereas candy and soda are high in added sugars.

Carbohydrate digestion

Starches and disaccharides are too large to be absorbed by your body. Therefore, they are broken down into smaller sugar molecules by enzymes produced in the digestive tract:

Sucrase: breaks down sucrose into 1 glucose and 1 fructose molecule. Lactase: breaks down lactose into 1 glucose and 1 galactose molecule. Amylase: breaks down starch into maltose.

Maltase: breaks down maltose into 2 glucose molecules.

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Carbohydrate absorption

Once starches and disaccharides have been broken down into simple sugars, they are absorbed by your digestive tract and transported into the bloodstream, where glucose causes an immediate rise in blood sugar.

This signals your pancreas to release insulin to help move the sugar from the blood into your cells.

In people who don’t have diabetes, the sugar moves from the bloodstream into the cells before it gets too high. However, in prediabetes or diabetes, blood

sugar remains elevated due to insulin resistance or inadequate insulin production.

How much do carbs raise blood sugar?

All digestible carbs are broken down into glucose, which increases blood sugar. This is true of starches and both natural and refined sugars.

Indeed, one study found that blood sugar increased similarly in people who consumed an equal amount of honey, table sugar or high fructose corn syrup (42).

Exactly how much carbs raise blood sugar varies from person to person, even among those with prediabetes or diabetes.

Therefore, it’s best to test your own blood sugar immediately before eating food with a known quantity of carbs and retest an hour later to see how this affects you.

For instance, 3.5 ounces (100 grams) of cooked white rice has about 28 grams of carb, which will be broken down to sugar in your blood.

Ideally, you should aim to keep your blood sugar below 140 mg/dL (7.8 mmol/L), the level at which nerve damage has been found to occur.

Knowing how much carb your own system can handle is key to achieving healthy blood sugar control at all times.

Fiber has neutral or beneficial effects on blood sugar

Fiber is an indigestible form of carb found only in plants. Like starch, it is made up of chains of sugars linked together.

However, although your body produces specific enzymes to break down starch and large sugar molecules into individual sugar units, it can’t produce the enzymes needed to break down fiber. Instead, the fiber you eat passes through your digestive tract and into your colon (43).

Because it isn’t broken down into sugar, naturally occurring fiber won’t raise your blood sugar. However, it can have either neutral or beneficial effects depending what type of fiber it is.

There are two broad categories of fiber: insoluble and soluble. Nearly every food contains both types, although in varied amounts and proportions.

About two-thirds of all the fiber you consume is insoluble, while the other third is soluble.

Insoluble fiber

Insoluble fiber doesn’t dissolve in water. However it does absorb water, which can help bulk up your stools and reduce constipation.

Since insoluble fiber simply passes through your system, it provides no calories and has no effect on blood sugar or insulin levels.

Foods high in insoluble fiber:

  • Oat, wheat and corn bran

  • Chia seeds

  • Avocados

  • Apples

  • Raspberries

  • Nuts

Soluble fiber

Soluble fiber dissolves in water and forms a gel that slows down food’s movement through your system, which can prevent blood sugar from rising too quickly and also help you feel full.

Once soluble fiber arrives in your colon, it is fermented into short-chain fatty acids (SCFAs) by the bacteria that live in your gut. Unlike insoluble fiber, which provides no calories, soluble fiber has been shown to provide 1-2 calories per gram due to being fermented into SCFAS (44).

However, this works out to only 6-10 calories for a serving of food containing 3-5 grams of soluble fiber, which is considered quite high.

What’s more, there is a lot of evidence suggesting that soluble fiber’s effects in the gut may help lower blood sugar and insulin levels, in addition to supporting colon health (45, 46, 47, 48).

Foods high in soluble fiber:

  • Artichokes

  • Avocados

  • Blackberries

  • Beans and legumes

  • Flaxseed

  • Spinach

You only need to count digestible carbs

Since fiber from whole foods does not increase blood sugar, it can be subtracted from the total carb amount to get the digestible or “net” carbs.

For example, a 3.5-ounce (100 grams) serving of blackberries contains 10 grams of carb and 5 grams of fiber. Therefore, it provides 5 grams of net carbs.

Importantly, certain packaged foods contain processed fiber that can be partially broken down into sugar and absorbed by your digestive tract. This may increase blood sugar levels similarly to starches and sugars.

One processed fiber that has been shown to raise blood sugar is isomaltooligosaccharide, which is found in some low-carb protein bars and other products (49, 50).

This is one of many examples why eating mostly whole foods rather than processed ones makes a lot of sense. Indeed, including whole foods rich in fiber at each meal can help improve blood sugar control while keeping you full and satisfied.

Protein’s effect on blood sugar is complex

Getting enough protein is incredibly important for staying healthy and looking and feeling your best.

Indeed, your skin, muscles and other organs are mainly made up of protein. In addition, proteins perform other important roles in your body, including functioning as hormones, enzymes and transporters of nutrients.

Protein is made up of long chains of amino acids, which are considered the building blocks of protein.

There are 22 amino acids in total. Of these, 9 are considered “essential,” meaning they must be consumed in food because your body can’t make them.

Proteins found in animal foods are described as being “complete” because they contain all of the essential amino acids in the quantities your body needs. By contrast, plant proteins lack sufficient amounts of one or more essential amino acid and are considered “incomplete.”

High-protein diets have been shown to suppress appetite, help you feel full and satisfied, boost calorie burning and protect muscle mass during weight loss (51, 52, 53, 54).

However, the effect of high protein intake on blood sugar isn’t as straightforward because of the way your body processes amino acids.

Protein digestion and absorption

After protein is consumed, it is broken down into smaller molecules called peptides by enzymes in your digestive tract. These peptides are absorbed into your small intestine.

Next, other digestive enzymes break these peptides into individual amino acids, which move into the bloodstream.

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These amino acids are then transported to the liver, where they are mainly used to fuel muscle growth or to create specialized proteins like hormones and enzymes.

However, they can also be used to make sugar in a process known as gluconeogenesis, which translates to “making new glucose.”

Importantly, gluconeogenesis is a demand-driven process. This means it typically occurs when your body needs sugar, such as when blood sugar levels get low.

Amino acids stimulate the release of both glucagon and insulin

In people who don’t have diabetes, higher levels of amino acids signal the pancreas to produce the hormones glucagon and insulin.

Insulin is secreted in order to stimulate your muscle cells to take up amino acids, and glucagon is secreted to stimulate gluconeogenesis.

The release of these two opposing hormones ensures that the amino acids are used for muscle health and that the blood sugar doesn’t drop too low. As a result, blood sugar levels remain stable after protein consumption.

In this way, the insulin and glucagon basically cancel each other out in terms of their effect on blood sugar.

What happens in diabetes?

In people with type 1 diabetes or type 2 that has progressed to pancreatic beta cell failure, insulin isn’t produced when amino acid concentrations rise.

However, the pancreatic alpha cells still produce glucagon.

When there is no insulin available to balance the glucagon, blood sugar levels may rise as gluconeogenesis continues.

Importantly, blood sugar rises much less after eating protein than after consuming an equal amount of carbohydrates. In addition, it increases more gradually over several hours, in contrast to the rapid rise that occurs within an hour or so of eating carbs.

What’s more, in people with prediabetes or diabetes who have insulin resistance, blood sugar levels seem to remain stable after eating protein.

How much protein can you eat if you have diabetes?

Interestingly, researchers have shown that relatively high protein doesn’t seem to cause problems in most people with diabetes and may even decrease blood sugar levels.

However, this depends on how much protein is eaten and whether it is consumed alone or with carbs. Studies suggest that pure protein doesn’t increase blood sugar much, if at all (55, 56, 57).

In a small study, 9 people with type 2 diabetes were given 50 grams of protein, 50 grams of glucose, or 50 grams of both on three separate occasions.

Researchers then looked at their blood sugar and insulin responses over the next 5 hours (55).

When protein was consumed alone, blood sugar remained stable and began to decrease 2 hours later. When protein and glucose were consumed together, initially the blood sugar increased. However, in the final hours of the study, blood sugar levels were 34% lower, on average, for the protein-glucose combination vs. glucose alone (55).

Research has shown that diets higher in protein and lower in carbs may lead to reductions in blood sugar levels, hemoglobin A1c values and insulin resistance in people with type 2 diabetes (58, 59, 60, 61, 62).

In addition, a recent study found that people with type 1 diabetes were able to consume up to 50 grams of pure protein without experiencing significant increases in blood sugar (63).

However, responses may vary from person to person, and type 1’s may need to adjust their insulin dosage when consuming high-protein meals.

Overall, studies suggests that protein intake of around 100 grams per day seems beneficial for people with diabetes. Given protein’s many healthful effects, intentionally restricting the amount of protein you eat isn’t a good idea.

Moreover, following a moderately high-protein, low-carb diet can help you achieve optimal blood sugar levels.

Fat’s effects on blood sugar are varied

Dietary fat adds flavor and a luxurious texture to food. It’s also a great source of energy. In fact, at 9 calories per gram, it provides more than twice as much energy as carbs or protein, which have 4 calories per gram.

There are three broad categories of fats based on their molecular structure:

  1. Saturated fats: Contain no double bonds between carbons in their fatty acid chains. Stearic acid is an example of a common saturated fat found in meat, dairy products and cocoa.

  1. Monounsaturated fats: Contain one double bond between carbons in their fatty chain. Oleic acid is the most common monounsaturated fat. Olive oil, nuts and avocados are excellent sources.

  1. Polyunsaturated fats: Contain more than one double bond between carbons in their fatty chain. The two families of polyunsaturated fats are omega-3 and omega-6.

    • Omega-3 fatty acids: A fatty acid with the first double bond occurring at the 3rd carbon. Alpha-linoleic acid is considered an essential fat because your body can’t make it on its own, so it must be consumed in your diet. Good sources include walnuts, flaxseed, pumpkin seeds and chia seeds.

    • Omega-6 fatty acids: A fatty acid with the first double bond occurring at the 6th carbon. Linoleic acid is the other essential fat you need to consume in your diet. It is found in many plant and animal foods, including meat, vegetables, nuts and seed oils.

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In addition, fats are classified by chain length:

  1. Short-chain fatty acids: Contain less than 6 carbons in their chain and are found in very small amounts in cream and butter.

  1. Medium-chain fatty acids: Contain 6-12 carbons in their chain. These saturated fats are also known as medium-chain triglycerides (MCT). They

are found mainly in coconut oil, palm oil and MCT oil.

  1. Long-chain fatty acids: Contain 14 or more carbons in their chain and are the most common types of fat. Saturated and monounsaturated long-chain fatty acids can be found in many foods, and fatty fish is an

excellent source of the long-chain omega-3 polyunsaturated fats EPA and DHA.

The fat you eat comes in the form of triglycerides, which contain three fatty acids joined together by a glycerol molecule.

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Fat digestion and absorption

In your digestive tract, enzymes break down triglycerides into free fatty acids and glycerol. The free fatty acids are transported into the bloodstream, where they are packaged with cholesterol, other fats and protein carriers to move throughout your system.

The glycerol can be taken up by the liver and used for gluconeogenesis if needed, similar to the way amino acids from protein are used. However, glycerol


is a small molecule that doesn’t contribute as much to gluconeogenesis as amino acids do.

In fact, the fat you eat has very little effect on your blood sugar on its own.

However, when eaten with certain foods, fat may have a strong impact on your blood sugar and insulin response, depending on the type and amount consumed.

Fat’s effect on blood sugar following mixed meals

Eating fat with high-carb foods is known to slow down the absorption of sugar into your bloodstream.

Although this may help prevent rapid blood sugar spikes after a large meal, the elevated blood sugar that appears later may last for several hours, along with a decrease in insulin sensitivity. This has been verified by studies in individuals with type 1 diabetes (64, 65).

In addition, high-carb, high-fat meals have been shown to promote inflammation and increase blood sugar and insulin levels in people with type 2 diabetes (66, 67, 68).

Effects of specific fats on blood sugar and insulin response

Research suggests that you may be better off choosing certain fats over others when consuming mixed meals:

  • Saturated fats: The combination of saturated fats and carbs seems to worsen blood sugar and insulin response. One study found that adding 2-3 ounces (50-100 grams) of butter to a potato significantly increased insulin levels in people with type 2 diabetes, whereas adding similar amounts of olive oil did not (69, 70, 71).

  • Monounsaturated fats: These fats have shown mainly favorable effects on diabetic health markers. In a study of 27 adults with type 2 diabetes, a weight loss diet high in monounsaturated fat led to significantly lower blood sugar and A1c values compared to a standard weight loss diet (69,

72, 73).

  • Omega-3 fats: The long-chain omega-3 fatty acids DHA and EPA found in fatty fish seem to lower blood sugar and reduce inflammation in diabetic individuals (74, 75).

  • Medium-chain triglycerides: Some studies have shown that medium-chain fatty acids improve insulin sensitivity. One study also

reported weight loss and decreased belly fat in overweight people with type 2 diabetes whose diets were supplemented with MCTs (76, 77).

  • Trans fats: Trans fats are artificially created by adding hydrogen to unsaturated fats to make them more stable and extend their shelf life. Trans fats have been linked to inflammation, insulin resistance and excess belly fat (71, 78).

When eating carbs and fat together, it appears that the more fat you consume, the more likely you are to experience high blood sugar and insulin levels for extended periods of time.

On the other hand, high-fat, very-low-carb ketogenic diets have been shown to improve several diabetes health markers, including lowering fasting blood sugar and A1c. This is true for both ketogenic diets rich in monounsaturated fats and those relatively high in saturated fat (79, 80, 81).

Essentially, cutting back on carbs allows you to eat greater amounts of healthy fat while maintaining excellent blood sugar and insulin levels.

How other nutrients affect diabetes

It’s clear that the amount of carbs, protein and fat you eat can have a major impact on your blood sugar. However, the macronutrient composition of your diet isn’t the only thing that matters.

Vitamins and minerals also play crucial roles in regulating your blood sugar. These compounds are classified as micronutrients because they’re only required

in small amounts. Also, unlike macronutrients, they don’t provide any calories for your body to use as energy.

However, if you don’t get enough of these important nutrients, you’ll struggle to achieve good blood sugar control and overall health, no matter how low your carb intake is.

In addition, there are antioxidants in many whole foods that may help reduce blood sugar and insulin levels.


  • Vitamin C: Vitamin C has been shown to help fight inflammation and reduce disease risk. In one study of obese adults with type 2 diabetes, increasing vitamin C intake significantly reduced fasting blood sugar levels and inflammatory markers (82).

Diabetes-friendly food sources: Leafy greens, tomatoes, bell peppers, strawberries, citrus fruit

  • Vitamin D: Adequate vitamin D blood levels are important for keeping blood sugar under control, and many people with diabetes are deficient in this vitamin. In one study, people with type 2 diabetes who were given 50,000 IU of vitamin D weekly for 2 months experienced significant reductions in fasting blood sugar and insulin levels and improved insulin sensitivity (83).

Diabetes-friendly food sources: Fatty fish, beef liver, egg yolks, cheese


  • Magnesium: Magnesium is involved in more than 600 chemical reactions in your body, including those that transform the food you eat into energy. Studies suggest that increasing magnesium intake may reduce blood sugar levels in people with diabetes. What’s more, one study found that prediabetic adults with the highest magnesium intakes were 32% less likely to develop diabetes than those with the lowest intakes (84, 85).

Diabetes-friendly food sources: Spinach, nuts, seeds, fatty fish, avocado

  • Chromium: Chromium is a trace mineral, meaning it’s needed in extremely small amounts. However, it plays an important role in carb, protein and fat metabolism. In some studies, people with type 2 diabetes who took chromium supplements had significant decreases in blood sugar and insulin levels (86, 87).

Diabetes-friendly food sources: Broccoli, turkey, garlic, green beans


Polyphenols are compounds found in the pigments of fruits, vegetables, nuts, seeds and a few animal foods. They’re prized for providing antioxidant activity that helps protect your cells from damage.

Polyphenols that may be helpful for diabetes or prediabetes include:

  • Anthocyanin: Research suggests that anthocyanin found in pink, orange and red foods may improve insulin sensitivity in people with type 2 diabetes (88, 89).

Diabetes-friendly food sources: Strawberries, tomatoes, salmon, shrimp

  • Catechins: These antioxidants are found mainly in tea and have been shown to reduce hemoglobin A1c levels in people with diabetes and prediabetes in some studies (90, 91).

Diabetes-friendly food sources: Green and white tea, blackberries

  • Resveratrol: Several years ago, this antioxidant found in purple and blue foods received a lot of media attention for its potential benefits on heart health. Recent research suggests it may also lower blood sugar and insulin levels in people with prediabetes and type 2 diabetes (92, 93).

Diabetes-friendly food sources: Blueberries, cranberries, cocoa and dark chocolate

It may seem a bit overwhelming to learn that there are so many components in food that can have such a strong influence on your blood sugar and insulin response.

Fortunately, sticking to whole foods that are low in carbs can help you meet your micronutrient needs and boost your antioxidant levels while keeping your diabetes under great control.

On the other hand, consuming processed foods that are carb-rich but

nutrient-poor is likely to trigger major blood sugar and insulin issues. You’ll find out more about this in the next section.

Does the modern western diet cause diabetes?

Can consuming a typical modern Western diet lead to diabetes? As you learned in Part 1, there are a number of risk factors that increase your risk of developing diabetes — including several related to lifestyle.

Based on the research available, it seems entirely possible that our modern diet has played a large role in the diabetes epidemic.

Dietary changes linked to increased diabetes risk

High sugar intake

A few hundred years ago, people didn’t eat much sugar at all. Wealthy individuals may have used small amounts of honey occasionally, but the working classes rarely consumed it because it was expensive and hard to find.

After mass production of refined sugar began in the 1700s, it became more widely available to everyone. Still, the average person in England only consumed about 18 pounds (8.1 kg) of sugar per year in 1800 (94).

However, within the past 150 years, sugar intake has steadily increased in the US and Europe, which has paralleled the obesity epidemic. In fact, the average person in the US currently consumes almost 150 pounds (67.6 kg) of sugar (including high-fructose corn syrup) per year (94).

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And although being obese is a risk factor for diabetes, high sugar intake may increase your chances of becoming diabetic even if it doesn’t lead to weight gain.

For instance, in India and certain Asian countries, increased sugar intake has been linked to rising diabetes rates, whereas obesity remains fairly uncommon (95).

Back in 2013, researchers looked at sugar intake and diabetes prevalence in 175 countries. They concluded that for every 150 extra daily calories consumed as sugar, a 1.1% increase in diabetes would be expected, regardless of other dietary or lifestyle factors (95).

Although this may not sound like much, for the current US population of 326 million people, this would mean that roughly 3.6 million people could develop

diabetes by consuming 150 extra sugar calories per day — the amount found in 12 ounces (340 grams) of soda or fruit juice.

Importantly, this was an observational study, meaning it can’t show that eating larger amounts of sugar directly causes an increase in diabetes.

However, there’s evidence suggesting that sugar can cause or worsen insulin resistance, one of the hallmarks of type 2 diabetes. And in the case of

sugar-sweetened beverages, this can happen pretty quickly.

In a 10-week study, when overweight and obese adults consumed 25% of calories from high-fructose beverages without increasing their overall calorie intake, they experienced an increase in insulin resistance and abdominal fat storage (96).

In addition, research suggests that high sugar intake may also increase the odds that those at high risk of type 1 diabetes will go on to develop the disease (97).

High intake of carbs, especially refined carbs

Foods made from refined flour make up a large portion of many diets today.

In addition to providing fewer nutrients and less fiber than whole grains due to the refining process, refined grains also seem to increase diabetes risk.

Indeed, several studies have linked increased consumption of processed grains to insulin resistance and type 2 diabetes (98, 99, 100).

Researchers report that between 1980 and 1997, American daily calorie intake increased by about 500 calories. Nearly 80% of this increase was carbohydrates, mainly the refined type found in breakfast cereals, white bread and snack foods like crackers and chips (100).

During this same time period, the number of people who developed type 2 diabetes increased by 47% (100).

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In addition, prediabetes rates have significantly increased within the past few decades as well.

Again, this is observational research. However, the results suggest a strong connection between higher refined carb intake and diabetes.

Unhealthy omega-6 to omega-3 fatty acid ratio

Our ratio of omega-3 to omega-6 fatty acids has changed dramatically over the past century, and not for the better. As you’ll recall, omega-3 and omega-6 are the two families of polyunsaturated fatty acids. Consuming them in the right balance is important for maintaining good health.

This is because many omega-6 fats have inflammatory effects, whereas omega-3 fats are anti-inflammatory.

A small amount of inflammation is necessary because it helps your body mount an immune response and aids in the healing process when you’re injured.

However, too much inflammation can cause all kinds of problems.

Our main fat sources prior to the development of industrial vegetable and seed oils were butter, cream, lard, tallow and olive oil. We also ate more fish and naturally raised animals with higher omega-3 fatty acid content (101).

Researchers have reported that in the past, people’s ratio of omega-6 to omega-3 fat intake was close to 1:1. However, our reliance on processed foods

and seed oils has resulted in a substantial increase in this ratio, which is currently estimated at a whopping 16:1 (102).

This change could very well be contributing to the diabetes epidemic, as inflammation is a major driver of insulin resistance and diabetes progression (103).

Other aspects of our modern lifestyle can increase risk

Our diet likely isn’t the only part of today’s busy lifestyle that’s responsible for rising diabetes rates.

Inadequate sleep, sedentary behaviors, stress, pollution and other factors definitely seem to play a role.

However, returning to a way of eating based on low carb, minimally processed foods may go a long way toward reversing the diabetes epidemic, reducing disease risk and increasing quality of life.

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