Why Smoothies Aren’t the Same as Eating the Same Food

SmoothiesPeople are busy. I “get” that, and morning routines are often the most challenging. Taking time to have breakfast is often seen as “one more thing to do”, so the idea of smoothies and “taking it with” may seem like a good idea. But is it? Are smoothies the same as eating the foods it is made out of? It isn’t.

Smoothies As Processed Food

In an earlier article, I covered the effect of various types of food processing (including mechanical processing such as pureeing fruit in a smoothie) on blood glucose. While 60g of whole apple, 60 g of apple that has been pureed, and 60g of apple that has been juiced have the same amount of amount of carbohydrate and a very similar Glycemic Index (GI) [1], neither the carbohydrate content nor GI tell us anything about how high blood sugar is going to go when eating or drinking them. Glycemic Index only indicates how slowly or quickly foods will increase blood sugar, not how much higher blood sugar will go [2].

A raw apple has a GI of 36  ± 2, and apple juice has a GI of 41  ± 2, so factoring in the error range, raw apple can have a GI of 38, and apple juice a GI of 39. A medium apple (3″ across) has ~25 g of carbs, and even when we make it into unsweetened apple sauce, it still has the same amount of carbs. If we press it into juice, the amount of carbohydrate in it doesn’t change. But we know from a 1977 study published in the Lancet that when fruit is pureed fruit or juiced and then eaten, the glucose response 90 minutes later is significantly higher, than if the fruit were eaten whole [3]. This is because the blender or juicer has done some of the work of digesting the food for us! That is what happens with smoothies. 

What’s Different About Smoothies? 

Most people think that digestion begins in the stomach, but it doesn’t. It begins in the mouth when we chew food.

When we eat a bowl of berries for example, chewing makes the glucose (sugar) in the berries that we chewed more available to the body — but when we put the same amount of berries in a blender and whir them up into smoothies, the contents of all the berries are now completely available for the body to act on. We never chew food as fine as a blender makes it, so blending food results in a faster spike in blood sugar than the whole food, eaten intact. This is one reason why drinking smoothies is not the same as eating the same food it is made from.

The order we eat foods in during a meal also makes a big difference on blood sugar and on the insulin response to eating (or drinking) carbohydrate-containing food. We know from a 2015 study about the effect of food order on the response of glucose and insulin that if the carbohydrate-containing food is eaten last, the glucose curve will be ~74% smaller than if it were eaten first! Likewise, if we eat the carbohydrate-containing food last, the insulin spike will be 49% smaller, than if we eat it first [4]!

Having smoothies for breakfast instead of a meal made out of the same foods means there is no way of having the carbs last!

Final Thoughts…

It really doesn’t take very long to eat the some veggies (like snap peas or baby carrots) and a dish of yogurt and berries for breakfast and the response on blood sugar and demand on our pancreas for insulin is significant!  This is why I tell people who come to me seeking to loose weight and improve their metabolic health to eat their food, not drink it at smoothies — because it does matter!

Making smoothiesThis is also one of the reasons that I felt Diabetes Canada’s “7-day Low Carb Meal Plan” which had a 30g of carbs (and only 9 g of protein) was not the best recommendation for people with diabetes to have for breakfast 3 days per week.

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  1. Atkinson FS, Foster-Powell K, Brand-Miller JC, ”International tables of glycemic index and glycemic load values”, Diabetes Care 31(12); 2281-2283
  2. Harvard Health Publishing, Glycemic index for 60+ foods (from American Diabetes Association, 2008), https://www.health.harvard.edu/diseases-and-conditions/glycemic-index-and-glycemic-load-for-100-foods
  3. Haber GB, Heaton KW, Murphy D, Burroughs LF. Depletion and disruption of dietary fibre. Effects on satiety, plasma-glucose, and serum-insulin. Lancet. 1977 Oct 1;2(8040):679-82. doi: 10.1016/s0140-6736(77)90494-9. PMID: 71495
  4. Shukla AP, Iliescu RG, Thomas CE, Aronne LJ. Food Order Has a Significant Impact on Postprandial Glucose and Insulin Levels. Diabetes Care. 2015;38(7):e98-e99. doi:10.2337/dc15-0429


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