CrossFit | A Systematic Review of Evidence on the Use of Very Low Calorie Diets in People with Diabetes

A Systematic Review of Evidence on the Use of Very Low Calorie Diets in People with Diabetes

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ByCrossFit May 16, 2019

This 2017 review surveys 17 trials that tested the effects of a very low calorie diet (VLCD) on people with diabetes. A VLCD is defined as a diet of fewer than 800 calories per day.

These 17 trials, published from 1986 to 2012, vary widely in design; daily calorie intake ranged from as low as 300 calories to as high as 800 calories, and trials ranged from as few as eight days to as many as six months. As such, summary statistics (i.e., the mean impact of a VLCD across all studies on specific biomarkers) were not calculated.

Seven of 14 trials that looked at fasting glucose showed that a VLCD led to significant improvements, while three of four found the same for fasting insulin. Nine studies looked at blood pressure, and all showed significant improvements. Ten of 14 studies that tracked blood lipids showed significant reductions in total cholesterol and triglyceride levels. No adverse effects linked to VLCDs were reported, though dropout rates ranged from 4.7% to 33%. (Note: Higher dropout rates were seen in longer trials.)

This review shows the difficulty of using existing evidence to clearly assess the impact of a VLCD on diabetes, in large part because the parameters of a VLCD have not been consistently defined. However, the review also shows that a number of trials using VLCDs demonstrated rapid, clinically meaningful improvements in metabolic markers that were sustained even after the VLCD concluded.

For example, four trials showed large improvements in fasting glucose and HbA1c due to a VLCD. In brief, these trials are:

  • Henry et al., 1986: A 300-calorie/d diet for 36 days decreased fasting glucose from 16.2 mmol/L to 5.3 mmol/L and HbA1c from 13.1% to 8.8%;
  • Wing et al., 1991: A 400-calorie/d diet for eight weeks decreased fasting glucose from 14.2 mmol/L to 7.7 mmol/L and HbA1c from 10.4% to 7.3%;
  • Kelley et al., 1993: A 400- to 800-calorie/d diet for three months decreased fasting glucose from 223 mg/dL to 109 mg/dL and HbA1c from 8.8% to 6.3%;
  • Snel et al., 2011: A 450-kcal/d diet for four months decreased fasting glucose from 12.1 mmol/L to 7.7 mmol/L and HbA1c from 7.8% to 6.7%. When this diet was combined with exercise, fasting glucose fell to 6.6 mmol/L and HbA1c to 6.3%.

Similar interventions may provide safe, rapid improvements in diabetes, particularly when paired with proper protein dosing and resistance training to prevent muscle loss.

Comments on A Systematic Review of Evidence on the Use of Very Low Calorie Diets in People with Diabetes

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Gary Taubes
May 17th, 2019 at 3:29 pm
Commented on: A Systematic Review of Evidence on the Use of Very Low Calorie Diets in People with Diabetes

Michael's and Dr. Eades's comments together raise what I consider the obvious issue with these VLCD's. Ok, so they work to put diabetes in remission. Do they do so because they reduce calories significantly or because they also restrict dramatically the consumption of the macronutrients that make up total calories? So maybe they work because they restrict protein or fat or carbohydrate consumption? The latter, or maybe the latter two, would be my guess. (I have a one-track mind.)


A 300 kcal/day VLCD is going to be at most 150 kcal/day of carbs, which means borderline ketogenic. A protein sparing modified fast of the kind the Eades used, as Mary Dan noted, is ketogenic. As designed originally by Bistrian and Blackburn it was 600 to 800 kcal/day of only meat, fish or fowl. Hence, the only carbohydrates came from the glycogen in these foods, maybe five percent of the calories. Protein content was high as a proportion of calories but very low in absolute terms.


One way to test whether the benefits of the VLCD were from the calorie reduction or the carbohydrates would be to fix the carbohydrate at that of the VLCD and then add fat back to increase the calories -- i.e., do what the Eades did. Or what Virta Health has been doing. The fact that the benefits seem to be identical suggests that it's the carbs not the calories. And now you have a relatively high-calorie ketogenic diet which is not only way more fun than starvation (whether or not it's way more fun than eating donuts and drinking beer), and way more sustainable. Perhaps even way healthier.


In a functional science, the researchers would be asking these kinds of questions: now that we've observed a benefit from these very low-calorie diets, what's the mechanism? What are reasonable explanations and can any of them be ruled out by this data?

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Matthieu Dubreucq
January 26th, 2020 at 12:50 pm

Thanks for the added information on VLCD

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Mary Dan Eades
May 17th, 2019 at 1:50 pm
Commented on: A Systematic Review of Evidence on the Use of Very Low Calorie Diets in People with Diabetes

In our clinic, back in the late 80s and early 90s, we used a VLCD frequently as a tool to help overweight, often diabetic or borderline diabetic patients lose weight and regain metabolic control. The variant we used was a PSMF (protein-sparing modified fast) involving consuming several protein shakes each day, restricted in carbohydrate and fat, coupled with a single (what would now be called 'keto') meal.


Initially we used a regimen of only the protein/low carb shakes and no 'solid' food (similar to what Oprah famously did on the Optifast program). It works very well as any VLCD will work very well, almost no matter what its composition. When calories are that low, it just about doesn't matter what they're made of as the body will use every single one of them and the metabolism will heal. (Granted, as this review points out, the numbers are almost always significantly better if the content is adequate in protein and restricted in carb).


So, just shakes works well and is very simple and straightforward for patients to use, if very boring. And it's a helpful tool for those patients (and there are quite a few) who have a fraught relationship with food; for them it removes the risk of error on what to eat and how much. One drawback, though, is cost, not that the shakes themselves are expensive, but rather since formula diets, such as an 800 VLCD, require some ongoing medical supervision for safety.


But after working with a lot of patients on this kind of regimen, we quickly came to see that the lion's share of the benefits of the PSMF on weight reduction and metabolic healing could still be had with the addition of a single tasty, savory meal providing protein and fat, with reduced carb to accompany the shakes. The meal content was pretty much like what CrossFitters are familiar with: meat, vegetables, nuts and seeds, some fruit, little starch and no sugar. And adding it bumps up the calories to something more like 1200 or maybe 1500 a day and makes the regimen much safer and easier to stay with longer term.


Plus the addition of fat in the meal encourages the gall bladder to work daily and sharply reduces the chance of stone formation that is a risk on any long-term very low fat diet.


Mike wrote his first book, called Thin So Fast, in 1989 about how to safely undertake a PSMF + meal plan on your own and put the tool into the hands of people outside a rigorous hospital or clinical setting. That book was, interestingly enough, the first time so far as we've been able to determine that the phenomenon of 'insulin resistance' was introduced to the lay public.


A VLCD is a tool, like any diet is a tool, used to tackle a task at hand. And it works well. (But then so does whole food keto, and as Michael Thalmann succinctly commented, that's waaayy more fun!)

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Elizabeth Flores
May 19th, 2019 at 10:12 pm


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Elizabeth Flores
May 19th, 2019 at 10:13 pm


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MIchael Thalmann
May 17th, 2019 at 5:49 am
Commented on: A Systematic Review of Evidence on the Use of Very Low Calorie Diets in People with Diabetes

Yeah, but keto is waaayy more fun than starvation 🤪

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