Understanding Digestion: Why You Should Eat Carbohydrates With Fat, Fibre, and Vinegar – IDM III

By Jason Fung, MD

In our previous post we discussed how the rate of digestion of different carbohydrates can affect our blood sugar levels.  Carbohydrates are chains of sugars.  They used to be classified by simple (1-2 sugars) versus complex (long chains).  This was not very useful because it did not help us figure out the speed of digestion.

The body breaks down different carbohydrates at varying rates.  We want to eat carbohydrates that take the body a long time to break down and to digest.  Understanding the digestion process of different foods can help you make better food selections.  Every time you go to pick-up a food item you should ask yourself “How is my body going to digest this food?” Being able to answer that question is crucial to your overall health.


Rate of Digestion of Processed and Refined Carbohydrates

Refined and processed carbohydrates are usually very easy for the body to digest.  During the refining process,  fats and fibre are generally removed.  Both fat and fibre, when eaten with carbohydrate tend to slow down the absorption of sugar and insulin spikes.

Common Types of Refined and Processed Carbohydrates to Avoid:

Sugar, wheat flour, bread, bagels, pasta, crackers, beer, sodas, diet sodas, fruit juices, cookies, candies, corn, corn flour, corn syrups, polished white rice, and alcohol sugars.

Rate of Digestion of Unrefined Carbohydrates

The carbohydrates found in foods like unprocessed grains, whole fruits and vegetables, are composed of many different sugar molecules linked together.  Their rate of digestion varies greatly depending on the composition of their simple sugar molecules.

Unprocessed grains like quinoa, barley, spelt and buckwheat, and starches like root vegetables, bananas and grapes, are composed of branching chains of glucose molecules that are easily digestible by the body.  These foods should not be consumed infrequently and in moderation (1).

Vegetables grown above the found, legumes, lentils, and fruits with their skins intact, are much more difficult for the body to digest.  They tend to be very high in fibre.  These types of carbohydrates should be the primary source of carbohydrates in your diet (2).

Fibre – A Protective Carbohydrate 

Fibre is a special type of carbohydrate because the body cannot break it down into its simple sugar molecules.  Fibre is also responsible for making you feel fuller, longer.  There are two main types of dietary fibre: insoluble and soluble fibre (3).

Insoluble fibre cannot dissolve in water.  It is also considered to be nature’s laxative because it helps move foods through your digestive tract by bulking up your stools and making them softer, and easier to pass.  In days past, it was often called “roughage”.

Soluble fibre can dissolve in water.  In the prescience of water it forms a gel, which slows down the digestive process by delaying the emptying of your stomach contents.  This phenomenon makes your feel fuller, longer, and this delay helps stabilize blood sugar levels.

Foods that are Excellent Sources of Fibre:
Raspberries, blueberries, black berries, strawberries, apples, pears, avocados, spinach, broccoli and carrots.  

Natural Fats

Fats usually take the longest to digest.  Their digestion process is initiated in the mouth where they are prepared for digestion in the small intestine.  Fats are virtually left untouched in the stomach until they reach the small intestine, where they are broken down and absorbed by the body (4).
Examples of Natural Fats:
Butter, coconut oil, olive oil, animal meat, poultry, fish, unprocessed cheeses, nuts, seeds, avocados, and avocado oil.


Vinegars (acetic acid) slow down the digestive process because they inactivate the production of certain digestive enzymes responsible for carbohydrate digestion.  This makes it a lot more difficult for the body to breakdown carbohydrates when eaten along with vinegar.  The vinegar forces the body to release the simple sugars from those carbohydrates slowly into the bloodstream preventing blood sugar spikes (5).  This is why people started putting vinegar on foods like French fries.

How to Make Carbohydrates More Difficult for the Body to Digest

You want to make your foods complicated to digest.  The more complicated they are to digest, the slower the release of sugar into your bloodstream.  If you are going to eat carbohydrates, make sure you consume them with fibre, fat, and vinegar when you can.  Combining these foods is the best strategy you have to stabilize your blood sugar levels.

1.  Add Freshly Ground Flax and Chia Seeds to Everything

Freshly ground flax and chia seeds are jammed packed with fibre and healthy fats.  They can be added to almost anything: beverages, soups, salads, meats, fish steel cut oats, yoghurt, etc.

2.  Always Have a Side Dish of Vegetables With Your Meal

Non-starchy vegetables are a great way to add more fibre to any meal.  Try a side salad of vegetable greens or stir-fry with your meals to reduce the impact of carbohydrates and proteins on your blood sugar levels.  Not only will they stabilize your blood sugar levels, they will make you feel fuller for a longer period of time!

3.  Cook with More Coconut Oil and Olive Oil

Do not be afraid of fat!  Not only will eating fat help stabilize your blood sugar levels, it will also keep your insides feeling full and warm.  Use butter or coconut oil for cooking foods at high heat.  Olive oil can be used to cook foods from low to medium heat, and is also great for adding flavour and fat to uncooked foods and in salad dressings.  Coconut oil doesn’t always have to be cooked either.  It take be taken on its own by the spoonful, or added to coffee or tea instead of creamer.  Some people even enjoy blending a tablespoon of coconut oil into their coffee for a special drink.  Others say it fries eggs better than butter.  You can also add nuts to salads and stir-fries.  Nut butters taste great on fruit too!

4.  Use Vinegar Whenever You Can

Vinegars can be mixed with olive oil and seasoned to your particular taste preference to make a good marinade or salad dressing.  They can also be added to soups and used as a condiment to almost any food.

5.  Add Nuts to Salads and Stir-Fries

Nuts can give wonderful flavour to different salads and vegetable dishes, and are an excellent source of natural fat.

6.  Butter is Back!

Do not be afraid to let this former dietary “villain” back into your kitchen.  Butter is an excellent source of natural fat.

By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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