Low Carb Diets Part II: What If I Have Diabetes?

In last week's blog post, we talked about low carb diets, definitions, and whether they work for weight management.  Today we'll discuss low carb diets in people with diabetes: Are they beneficial? Are they safe?

As far as potential benefit goes, the available data are not consistent in their findings.  In a review article published by Feinman and colleagues in the journal Nutrition, data is summarized reporting an improvement in blood sugar control, along with a reduction in medications required to control blood sugars.  However, systematic reviews and meta analyses have not consistently shown improvements in blood sugar control.  At least some of the variability likely has to do with adherence - low carb diets are not easy to stick to for many people.

If a low carb diet is going to be embarked upon, the type of medication that a person with type 2 diabetes is taking to control blood sugars is very important to consider.   Medications that can cause low blood sugars [insulin; sulfonylureas such as gliclazide (Diamicron) and glyburide; and meglitinides (eg Gluconorm)] may need to be decreased with the help of your health care provider, in order to avoid low blood sugars.

SGLT2 inhibitors are a class of medications to treat type 2 diabetes, which are associated with a risk of 1 in 1000 people per year developing diabetic ketoacidosis (DKA), which is a type of acid buildup in the blood that is life threatening. For people on these medications [canagliflozin (Invokana), dapagliflozin (Forxiga), empagliflozin (Jardiance)], low carbohydrate diets are associated with an increased risk of DKA.  As to whether a mildly low carb diet is safe is not known, as there is very little data available in this area.  One small study did show an increase in ketones in people with type 2 diabetes on an SGLT2 inhibitor on just a very mildly restricted carbohydrate diet (40% calories, as compared to people on a 55% carb calorie diet), but how much this may increase the risk of DKA is not known.

A ketogenic diet should be avoided for anyone with type 2 diabetes on insulin or SGLT2 inhibitors, because of the risk of ketoacidosis.

For people with type 1 diabetes, there is very limited data on which to guide us.  There is some data suggesting that a low carb diet may improve hemoglobin A1C (a marker of blood sugar control).   However, there is a concern that there may be a blunted response to glucagon as an emergency treatment for severe low blood sugar in people with type 1 diabetes following a low carb diet.

A ketogenic diet should be avoided for anyone with type 1 diabetes due to the increased risk of ketoacidosis.

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Low Carb Diets - What Are They... And Do They Work?

One of the more currently in vogue weight management approaches is a low carbohydrate diet.  I get asked about this a lot, so I figured it's time to put my thoughts in e-print!  I'm going to take this in two parts.  Today's blog will be about low carb diets in general, and the second will be about the low carb diet in people with diabetes.

So, what is a low carb diet exactly?  Well, they have many names and forms: low carb, lower carb, very low carb, lower carb high/healthy fats (LCHF), ketogenic.  Definitions of each of these vary, making comparisons and scientific study challenging.  However, we can generally categorize these diets as follows:

Low Carb:

• providing less than 45% of the day's calories, OR
• less than 130g of carbs per day (= 520 calories)

Ketogenic or Very Low Carb: 

• maximum carbs of 20-50g per day

LCHF : (low carb, high/healthy fat)

• the amount of carbohydrate recommended varies, but would fall in the low carb zone as defined above
• the restriction in carb calories is replaced with healthy fat choices

So, does a carbohydrate restricted diet result in more effective weight management?   When compared to a low fat diet, the studies suggest that while there may be superior weight loss in the short term (eg 6 months), there is no difference after 1 year.   The bottom line of the extensive studies on dietary composition shows that there is no particular macronutrient composition (carbs vs protein vs fat) that is superior to another when it comes to weight loss.  

What is important is finding a permanent lifestyle change that works for each individual, and the composition of that diet is going to vary based on taste preferences, cultural differences and so forth.
I often hear of people feeling that they are being instructed to eat too many carbs, more than they actually want to eat.  Their health care providers are probably following the teachings of Canada's Food Guide (CFG), which many obesity experts (including myself) would argue advises a carbohydrate intake that is too high for many people at up to 65% of total daily caloric intake.   Remember that Canada's Food Guide (CFG) was designed for weight maintenance in adults, but that the majority of Canadian adults have overweight or obesity.  Ergo, the CFG is only applicable to a minority of Canadian adults.  Also, the average woman age 50+, and the average man age 70+, will gain weight following the CFG recommendations.

Most dietary guidelines recommend at least 45% carbohydrate, in order to limit excessive intake of saturated fat.  It is important that the fats in our diet are the healthier unsaturated fats - in fact, the Mediterranean style of eating, which provides 35-47% of calories as fat, has been shown to reduce the risk of cardiovascular disease and breast cancer.

For some people, a restricted carbohydrate intake may work well - it eliminates the option of grabbing many high calorie food items on the run (eg bakery, vending machine, coffee shop products and so forth).   There are also some people who may have an addiction-type response in their brain circuitry to high sugar foods, and avoiding these may help to break the cycle of overeating.  But it's definitely not for everyone.  

In terms of weight maintenance and prevention of weight gain after weight loss, there is evidence to suggest that a higher protein, lower glycemic index diet may be better than a lower protein, higher glycemic index diet. 

Stay tuned for part II: Can people with diabetes safely eat low carb?

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Diabetes Medication Canagliflozin Reduces Cardiovascular Events

The eagerly awaited results of the CANVAS trial were just released yesterday at the American Diabetes Association Meeting, and published simultaneously in the New England Journal of Medicine.

The CANVAS program was a cardiovascular outcome trial of the SGLT2 inhibitor, canagliflozin (Invokana).  This program enrolled 10,142 people with type 2 diabetes and high cardiovascular risk, and randomized them to receive either canagliflozin 100mg, canagliflozin 300mg, or placebo, in addition to their usual care.

After a mean of 3.6 years, they found that canagliflozin reduced the risk of a combination of cardiovascular death, non fatal heart attack and non fatal stroke by 14%, with the benefit being particular to those with established cardiovascular disease at baseline.  The individual outcomes above were not significantly reduced when considered separately, but were significant when considered together.   Canagliflozin also reduced the risk of hospitalization for congestive heart failure by 33%, reduced the risk of poor kidney outcomes by 40% (a composite of a sustained 40% reduction in GFR, need for renal replacement therapy, or death from renal causes), and reduced progression of albumin in the urine by 27%.

In terms of risks of canagliflozin, unexpectedly, there was an increase in the risk of amputation, with 3.3% of people on canagliflozin requiring an amputation (most commonly a toe or forefoot) during the course of the trial, vs 1.5% in the placebo group.    There was also an increase in the risk of fracture, with 15.4 fractures per 1000 patient years on canagliflozin, vs 11.9 per 1000 patient years in the placebo group.  There was an increased risk of genital yeast infection, as expected for this class of medications, but no increased risk of urinary tract infection.

The CANVAS program adds to our understanding of the SGLT2 class of medications.   As the EMPA REG trial showed us that the SGLT2 inhibitor empagliflozin (Jardiance) also reduces CV events in people with type 2 diabetes and cardiovascular disease, this is looking more likely to be a 'class effect' of the SGLT2 inhibitors (we still await the DECLARE study of the SGLT2 inhibitor dapagliflozin (Forxiga) to be completed).

In terms of the risks seen in the CANVAS trial, much discussion is underway in the medical and scientific community, and more studies will need to be done to better understand these findings.  As always, the benefit vs risk of any medication must be carefully considered in finding the best medications for each individual patient.


Disclaimer: I receive honoraria as as continuing medical education speaker and consultant from the makers of canagliflozin (Janssen), empagliflozin (Boehringer-Ingelheim and Lilly), and dapagliflozin (Astra Zeneca).  I am involved in research of SGLT2 inhibitors as a treatment of diabetes. 

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Are Calorie Equations Accurate In Obesity?

Some people who are working on losing weight like the approach of a calorie prescription, which is the daily amount of calories in food/drink that they should not exceed in order to lose weight.

This calorie prescription starts with an estimation of Resting Energy Expenditure (REE), which equals the number of calories we burn at rest over 24 hours, and can be estimated by any of a number of equations that have been developed for this purpose.  These equations incorporate various factors that influence REE, including age, gender, height, and weight.  From there, we typically multiply the REE by an activity factor to calculate the number of calories a person needs in a day, and then usually subtract 500 calories per day in order to achieve an initial rate of weight loss of around 1lb (0.5kg) per week.  

Most of these equations were generated using normal weight individuals, including very few people who carry excess weight.  But are these equations accurate in people with obesity?

A study, published in the International Journal of Obesity, evaluated a number of these formulae in 1,851 people with obesity, comparing the calculations to actual measures of Resting Energy Expenditure (using a technique called indirect calorimetry). 

They found that the accuracy of the equations to predict Resting Energy Expenditure was very low in people with obesity, and were even less accurate in people with a higher degree of obesity (BMI >40), especially females.   Even the Mifflin St-Jeor equation, commonly cited as the most accurate equation, performed poorly. These equations generally underestimated the calorie needs of participants by several hundred calories, with the degree of underestimation increasing with increasing BMI.

As these equations come in low, the calorie prescription ends up being too low.  This could mean that a person with obesity leaves their health care provider’s office with a calorie prescription that is too restricted – for example, that patient may be told that she should take in 1500 kcal per day in order to lose 1 lb per week, when actually her prescription should be 1900 kcal per day to lose 1lb per week.  For her, sticking to 1500 kcal per day would be very difficult – it may cause more rapid weight loss at the beginning but would be very tough to stick with.  

So why would these equations be less accurate in people with obesity? Fat tissue is less metabolically active than lean tissue (eg muscle), so having a higher proportion of fat can reduce accuracy of estimation using equations that were developed in a lean population.  It is also not clear which weight to use in these equations – actual weight, ideal weight, or adjusted weight.

Indirect calorimetry is a much better way to estimate calorie needs than equations, but has a price tag and limited availability. 

Clearly, we are in need of equations that are validated in people with obesity to estimate resting energy needs. 

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