The Standards of Medical Care for Diabetics contains the best practices at the time of publication based on the reading of the science. The following is from the (American Diabetes Association, Diabetes Care 2014 Jan; 37(Supplement 1): S14-S80. Standards of Medical Care in Diabetes—2014):
Carbohydrate Amount and Quality
Monitoring carbohydrate intake, whether by carbohydrate counting or experience-based estimation, remains a key strategy in achieving glycemic control. 
For good health, carbohydrate intake from vegetables, fruits, whole grains, legumes, and dairy products should be advised over intake from other carbohydrate sources, especially those that contain added fats, sugars, or sodium. 
Substituting low-glycemic load foods for higher-glycemic load foods may modestly improve glycemic control. 
People with diabetes should consume at least the amount of fiber and whole grains recommended for the general public. 
While substituting sucrose-containing foods for isocaloric amounts of other carbohydrates may have similar blood glucose effects, consumption should be minimized to avoid displacing nutrient-dense food choices. 
People with diabetes and those at risk for diabetes should limit or avoid intake of sugar-sweetened beverages (from any caloric sweetener including high-fructose corn syrup and sucrose) to reduce risk for weight gain and worsening of cardiometabolic risk profile. 
I added the numbers in square brackets above for commenting below:
- How many grams of carbs are you eating in a day? You need to track the grams of carbohydrate you are eating in a day. Tracking is not a pill and your doctor won’t do it for you. Unless you track you probably have no idea how many grams of carbohydrates you are eating in a day.
- Real sources of carbohydrates should be eaten rather than empty carbohydrate calories. An empty calorie is one that only provides calories with very little other nutritional value (vitamins, minerals, etc). Some of the listed items have more carbohydrates than others. Tracking will give an idea of how many grams each item has.
- Low Glycemic foods don’t increase your blood sugar as much as higher glycemic index foods. This guidance is helpful but most people don’t know what it means, including doctors.
- Eat fiber because it buffers the blood sugar rise you get from carbs in food. While I disagree with the need for whole grains they are certainly preferable to processed flour products.
- It’s obvious to most people that a cup of broccoli might have the same number of calories, or even grams of carbs, as a few jellybeans but the two are not of nearly the same value. This is not an IIFYM (If It Fits Your Macros) approach.
- Staying away from soda which has sugar avoids many problems. A single soda or two in a day can double your carbohydrates. Eat carbohydrates at a level which supports weight loss, not gain.
Note that there’s no upper or lower recommendations for carbohydrates here. A Very-Low Carbohydrate diet fits within these standards.
There are five studies of Low Carb diets which are listed in the references section of the standard. I think that a Standard of Care is pretty darned important. The standard of proof for studies used to make the Standard of Care should be high.
- Larsen RN, Mann NJ, Maclean E, Shaw JE. The effect of high-protein, low-carbohydrate diets in the treatment of type 2 diabetes: a 12 month randomised controlled trial. Diabetologia 2011;54:731–740
- Davis NJ, Tomuta N, Schechter C, et al. Comparative study of the effects of a 1-year dietary intervention of a low-carbohydrate diet versus a low-fat diet on weight and glycemic control in type 2 diabetes. Diabetes Care 2009;32:1147–1152
- Guldbrand H, Dizdar B, Bunjaku B, et al. In type 2 diabetes, randomisation to advice to follow a low-carbohydrate diet transiently improves glycaemic control compared with advice to follow a low-fat diet producing a similar weight loss. Diabetologia 2012;55:2118–2127
- Stern L, Iqbal N, Seshadri P, et al. The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: one-year follow-up of a randomized trial. Ann Intern Med 2004;140:778–785
- Shai I, Schwarzfuchs D, Henkin Y, et al., Dietary Intervention Randomized Controlled Trial (DIRECT) Group. Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet. N Engl J Med 2008;359:229–241
Let’s look closely at a couple of the studies for their weaknesses/strengths.
Larsen, et. al.
This may be the worst study I have ever seen referenced in anything important. The title of the study is misleading since the study did not even control for carbohydrates. This was not a metabolic ward study nor was compliance verified in any meaningful way. Dietary advice was given at the start and the results assessed 3, 6, and 12-months later. Further, there was no determination of what low-carb meant – although it appears to just mean not high-carb. In spite of that, the Conclusion stated:
These results suggest that there is no superior long-term metabolic benefit of a high-protein diet over a high-carbohydrate in the management of type 2 diabetes.
Nothing in the conclusions that support the title. In fact, someone who eats a “high-protein” diet may well be avoiding fat and eating low fat cuts of meat and eating high carbohydrate amounts. Looking closer at the actual data shows that at 12-months the High Protein group was eating 41.8% of calories from carbohydrates and 48.2% for the High Carbohydrate diet. That is hardly low carb levels.
Davis, et. al.
This was another poorly formulated study. In spite of that this study also found similar results between low-fat and low-carb diets. Once agaqin, dietary compliance was not done by putting people into a metabolic ward. Macros were checked by asking for the 24-hour food consumed – presumably from the day before.
Here’s the protocol. The flaws should be obvious:
- Participants signed up for the study.
- Participants were given nutritional advice as part of a study.
- Participants were interviewed at 6 and 12 months.
- Participants knew their appointment is coming up the next day to check on how they did with the diet.
- The researchers then asked Participants what they ate the day before.
Do you think that they followed the advice they were given a year earlier? Probably to the best of what they remember from the year before. And maybe they ate “better” that last day.
The real test is in the actual data. The Low Carb group said that they ate 1642 calories a day and the Low Fat group said that they ate 1810 calories a day (10% less calories is glossed over). The Low carb group ate 33.4% of their calories from fat (do you see a theme here?) and the Low Fat group said that they ate 50% of their calories from fat. Again, not really a test of a low carbohydrate diet. In spite of that, the “Low Carb” diet was no worse.
Guldbrand, et. al.
The macro levels used for this study were much closer to actual Low Carb levels (20% of calories from carbohydrate). The conclusions stated:
Weight changes did not differ between the diet groups, while insulin doses were reduced significantly more with the LCD at 6 months, when compliance was good. Thus, aiming for 20% of energy intake from carbohydrates is safe with respect to cardiovascular risk compared with the traditional LFD and this approach could constitute a treatment alternative.
This study was done in Sweden and may have been a part of the change to the Swedish dietary guidelines towards Low Carb.