To learn more about all that, including the actual diets, check out earlier parts to this series:
Click to read Can Type 2 Diabetes be Reversed
Click to read Very Low Calorie Diets & Type 2 Diabetes Reversal Part 1: Blood Glucose
Click to read Very Low Calorie Diets & Type 2 Diabetes Reversal Part 2: Insulin
Click to read Very Low Calorie Diets & Type 2 Diabetes Reversal Part 3: The Liver & Pancreas
Now that you’re caught up, or if you’ve been part of this journey all along, welcome back.
It’s great to know that very low calorie diets can bring fasting glucose down, and that it helps with insulin. Then again, you would expect eating less would make the job of dealing with what we eat easier on our bodies.
So what you really want to know is what happens after the diet. What would happen with a normal meal? There are a few main ways of testing this:
- Oral glucose tolerance;
- Intravenous glucose tolerance test; and
- Mixed meal test
Oral Glucose Tolerance Test
The oral glucose tolerance test is exactly that, you get given a glucose drink (the oral and glucose part of the name), and your blood glucose is measured before and after (the tolerance part).
Tests are done after an overnight fast. Blood glucose is measured to give a fasting blood glucose. The dose of glucose is commonly 75 g, but can sometimes be 50 g or 100 g. This has to be drunk within a 5 minute window.
The oral glucose tolerance test is used both in clinical practice to diagnose type 2 diabetes, and in research. The difference tends to be how often blood glucose is measured.
To diagnose type 2 diabetes, all that’s needed is a fasting blood glucose, and a blood glucose 2 hours after the glucose drink. In research you’ll often see blood glucose being measured at several time points throughout the 2 hours and sometimes after the two hours.
You may also see other things measured in the research setting, e.g. insulin response. Some examples of results for different levels of glucose tolerance are shown below.
With insulin the picture is different. The normal insulin sensitive person has an intermediate rise in insulin, and this is enough to get the job done.
The person with type 2 diabetes can’t produce enough insulin anymore. While the person with impaired glucose tolerance is topping the chart with insulin production. They can still produce quite a bit, but not fast enough to control blood glucose well.
There are also people with type 2 diabetes whose blood glucose is still going up after two hours, and who produce less insulin. But these graphs give you some idea of the differences in response.
Intravenous Glucose Tolerance
The intravenous glucose tolerance test is similar to the oral glucose tolerance test described above, but the glucose is injected into a vein (1-3).
The intravenous glucose tolerance test has its uses, but is somewhat artificial in that is avoids all the processes that happen with actually eating, so it doesn’t reflect a person’s response to food as well as the oral glucose tolerance test.
This test also isn’t used for diagnosis of type 2 diabetes. The information from this type of test informed part 3, so I won’t repeat it here.
Mixed Meal Test
Mixed meal tests arguably mimic real life more closely than either the oral or intravenous glucose tolerance test. Although the ‘meal’ in question often isn’t what most people would eat, often being some form of meal replacement drink (4,5).
What Happens to Glucose Tolerance After Very Low Calorie Diets?
I’ll use the name of the first author when discussing specific studies so that you can find the details of that study in the tables in previous parts in case you want more details about a given study (mostly Table 1). Unfortunately not many studies assessed glucose tolerance in a way that is accessible to most people.
Laferrére and colleagues (2008) did a three hour oral glucose tolerance test with 50 g of glucose (3). Two-hour glucose improved from 10.2 mmol/L to 9.6 mmol/L, which is fairly modest given that this wasn’t the typical 75 g glucose load used to diagnose the condition. Worth knowing is that the people in this study were still in the morbidly obese category (average BMI 43.3 reduced to 39.6).
Lingvay and colleagues (2013) used a mixed meal test, so again, you can’t compare it to the classic 75 g oral glucose tolerance test used for diagnosis (5). The graph below tells the story best.
The study by Lim and colleagues (2011) did a two-hour oral glucose tolerance test, but not until 12 weeks after people finished with the very low calorie diets, and after an average 3.1 kg (6.8 lbs) weight regain (6). Average fasting glucose was 6.1 mmol/L and 2 hour glucose 10.3 mmol/L, so volunteers were back at the high end of impaired glucose tolerance, at least on average.
How Long Does it all Last?
You stay fit/strong as long as you keep up the training that got you there. In fact it usually takes less effort to maintain a change than to make it in the first place. That same rule applies here.
Those few studies that reassessed their volunteers weeks or even months after the end of the diet send a mixed message.
Jonker and colleagues (2014) reassessed their volunteers 18 months after the diet (7). On the downside, weight, HbA1c, and fasting glucose, all went back up. On the upside they were still lower than before the diet, just not as low as immediately after it.
It’s interesting that the same study described in the paper by Snel and colleagues (2012) showed that along with the weight regain, liver fat and visceral fat also came back up after 18 months, although not as high as before the diet (8). You may remember from part 3 that liver response to insulin improved as liver fat went down.
This study also looked at many aspects of heart health and function, some of which remained improved at 18 months (7). The problem here is that volunteers ‘were reintroduced to a regular diet’ with no description of what that was.
A study by Jazet and colleagues (2007) had a more long-term focus in that insulin dependent volunteers were first put on a 30 day very low calorie diet (9).
Then volunteers were advised to slowly transition from having exclusively meal replacement drinks to having meals introduced at 1 meal (an extra 200 kcal/day) every 2-4 weeks (9). Their energy requirements were calculated and they were informed of these, but the volunteers were free to eat how they wanted, and saw their doctor every three months.
The results of this approach were a slightly lower (average) weight and therefore BMI at 18 months than immediately after the very low calorie diet (9). Unsurprisingly under the circumstances, improvements in fasting blood glucose and HbA1c were maintained for the full 18 months. Again these were the average result. Some volunteers regained weight and had to go back on insulin and/or other diabetes medication.
Of course there’s no reason why a very low calorie diet can only be done once. One study looked at two 12 week rounds of a very low calorie diet (400-500 kcal/day) separated by 12 weeks of a low calorie diet (1000-1200 kcal/day), and followed by another 12 weeks of low calorie diet (10).
The intermittent very low calorie diet group was compared to a low calorie diet group who were prescribed 1000-1200 kcal/day for the whole 48 weeks (10). Some key results are shown in the graphs below.
What you’ll also notice in the third graph is that greater weight reduction resulted in greater improvement in HbA1c (10).
What the published results can’t tell us is if the volunteers who stayed in the study, and not everyone did, actually followed the diet. The fact that weight and HbA1c went up toward the end, suggests that either discipline wavered – I know mine would – or that the volunteers energy requirements dipped below the 1000-1200 kcal/day they were consuming.
The longest running study assessed people five years after a very low calorie diet lasting six or more weeks as chosen by the volunteers (11). After the diet, volunteers were advised to eat a low fat, low refined carbohydrate diet; whether they did is unclear.
After five years this group were roughly where they started in terms of glucose, and weight and therefore BMI (11). The group that got intensive lifestyle counselling didn’t see any major improvements in the first year, but was better off at five years.
Interestingly, many people who reported following a very low calorie diet on their own (outside of research) also reported being diabetes free for longer than the volunteers in the studies discussed above (12). We don’t know how, or how long, because they aren’t being formally monitored.
These somewhat disappointing results demonstrate what the very first blog discussed – to think in terms of a ‘cure’ for type 2 diabetes is to ignore that type 2 diabetes is a miss-adaptation to environmental factors.
By that I mean the environment that the liver, pancreas, muscles, and other organs find themselves in, e.g. in terms of food and toxins. Change that environment sufficiently, and the symptoms will go away. But if it changes back sufficiently, the symptoms will reappear.
Bare in mind that most of these studies didn’t set out to teach volunteers the skills they would need to maintain their improvements.
In fact, I’d argue none of them did, because most researchers still held/hold to the idea that everyone, including those with type 2 diabetes, should eat a high carbohydrate low fat diet, when this really doesn’t make a lot of sense in a World where insulin resistance and glucose intolerance is fast becoming the norm (13,14).
Next week we’re taking a break from this series to look more closely at the importance of excess liver and pancreas fat to type 2 diabetes and address questions like why some people who aren’t obese get symptoms and some who are very obese don’t. We also begin to look beyond very low calorie diets for reversing type 2 diabetes.
Click here to read part 5.
References: click here for a full list of references
To learn more about type 2 diabetes and what you can do to better manage, and often reverse it, watch my free video education series. If you want one-on-one help dealing with your type 2 diabetes, contact me here to book a consultation.