Gut Bites MD

Christopher Damman, Associate Professor of Gastroenterology, School of Medicine, University of Washington. Editor-in-Chief of Gut Bites MD.

The science behind blood sugar and how fiber can impact the way energy is stored. More fiber and less sugar is the prescription for metabolic control. Some practical advice on how to increase fiber is provided at the end.

The science behind blood sugar and how fiber can impact the way energy is stored and used in the body.

Part 1 of this series focused on how appetite and nutrient absorption in the gut impact weight loss. To recap, the most powerful approaches to weight loss, including the drug GLP-1 and bariatric surgery, change the energy account balance and reset the metabolism set points. They both decrease appetite through hormones (less calories in), and in the case of surgery, increase the calories that don’t get absorbed (more calories out).[1] The good news is that consuming more fiber in our diets can be used as a complementary approach to weight loss as it decreases appetite through the same GLP-1 hormone pathway (less calories in) and makes food harder to digest (more calories out).[2,3]

But you might ask, what about ketogenic diets, intermittent fasting, non dietary approaches, and new high-tech personalized approaches to weight loss? Are these effective, how do they work, and how might fiber be a complement to these approaches? The common thread to all these weight loss measures is how blood sugar levels control the use (or storage) of calories inside the body. It turns out fiber also has a role to play here. Here’s how in a bite-sized overview of a feast-sized field.  

Keto: craze or credible?

The ketogenic diet aims to keep blood glucose levels very low by having you avoid eating carbohydrates and foods that have low or no glycemic index (fats and proteins).[4] The glycemic index refers to just how quickly and strongly various foods raise the sugar levels in your blood.[5] The higher these levels go, the more dramatically they stimulate insulin levels. Insulin is a hormone that, among other jobs, helps convert excess sugar to fatty acids that are stored largely in fat and liver cells. Higher blood sugar leads to higher insulin levels, which leads to more fat.[6]

A ketogenic diet keeps blood sugars low so your body has less access to this energy type. Your body instead taps into dietary and body fat to fuel itself. When fat is converted to energy, it creates ketone bodies. Unlike calorie restrictive diets that can make you more hungry, ketones actually help control your appetite so you eat less food (less calories in), and help maintain your body’s metabolic rate by preserving muscle over fat (calories burned).[7] The end result? You decrease fat in the body and lose weight. The data looks promising for ketogenic diets and some companies (e.g. Virta Health) are tapping into this powerful approach![10,11] There are some great resources on the web providing advice on how to follow a lower carbohydrate diet (e.g. Dr. Lori Shemek)

Of course, there remain questions as to how sustainable this diet might be in the long run.[12] There are also unresolved questions around whether a high fat diet might lead to high cholesterol and cardiovascular disease while a high protein diet might lead to stress on the kidneys in the long run.[13,14] A diet that balances higher amounts of plant-based fat and protein with lower amounts of animal-based nutrients may help prevent the potential long term risks of a ketogenic diet and be superior for health.[15,16]  Also there might be important lessons from traditional hunter gatherer societies that have alternating wet and dry seasons with alternating high carbohydrate  (berry and honey) and high protein (bush meat) diets.[17]

In excluding sugar and carbohydrates, it is also essential to not lose sight of the importance of fiber, which has very synergistic benefits with a keto diet. It is notable that fiber consumption (baobab fruit and tubers) remains constant across all seasons in hunter gatherer societies.[17]  Indeed, the butyrate made from fiber by the gut microbiome and the beta-hydroxybuturate (a ketone) made from fat in a keto diet, work in much the same way to control appetite, decrease blood sugar, and preserve muscle It is also important to note that fiber helps prevent constipation that is often associated with keto diets and may help prevent the long-term risks of colon, breast and prostate cancer associated with a low fiber diet.[19–21]

Intermittent fasting: proselytized or promising? 

So what about intermittent fasting, a group of several different diets that restrict eating to only some days of the week or hours of the day? (For practical advice on fasting and a discussion of different protocols, Beginners Guide to Intermittent Fasting.) This works in a very similar way to a keto diet but rather than an around-the-clock depletion of sugar from the blood, it intermittently triggers the body to use fat reserves instead of sugar. The end result is similar – a decrease in fat and improved weight loss.[22,23] Some think that a diet like this is more sustainable than a ketogenic diet because the rest of the time you can still consume a ‘regular diet’. This can be less socially limiting if you want to go out for a meal with friends and family.

The relative downside of intermittent fasting is that weight loss might be less dramatic than in a stricter ketogenic diet and some (although not all) studies have shown that it may contribute to muscle loss in certain settings.[24] Intermittent fasting in the setting of a high fiber diet might help mitigate against muscle loss as fiber and the molecules it stimulates (butyrate and GLP-1) have been shown to help prevent muscle wasting.[25,26] 

Staples beyond diet: exercise, stress reduction, and sleep

So what about weight loss measures beyond diet: exercise, stress reduction and sleep? It turns out all of these activities have direct effects on blood sugar as well and this is likely one major way they benefit weight loss. How? Exercise funnels blood glucose into muscle cells to burn instead of fat cells to store.[27] Exercise is especially useful within 15 minutes of a meal to help prevent spikes in glucose and insulin![28] Good sleep (aim for 8 hours per night) and stress reduction decrease your body’s production of natural steroids like cortisol that can increase appetite, blood sugar levels, insulin and fat![29,30]

New horizons in personalized blood sugar control

The new kids on the block in weight loss are continuous glucose monitors (e.g. Dexcom and Abbott). Originally developed for folks with diabetes, they provide a near real-time assessment of sugar levels in the blood to alert someone to make an immediate modification to diet and lifestyle factors.[31] While currently only available for those with diabetes through a prescription from their doctor, there is a lot of excitement to potentially one day soon use these devices in folks that don’t have diabetes.[32] Research is underway as to its usefulness and a number of companies (e.g. Levels Health) are banking on its success. 

Other companies (e.g. DayTwo and Zoe) have correlated specific stool microbiome signatures with blood sugar responses and make recommendations for eating based on a stool test. These personalized approaches to blood sugar control and weight loss could be game changers because it turns out that everyone’s response to foods in their blood sugar levels is different. Having real-time feedback could be invaluable for helping people choose the right foods!

We all need fiber, fast!

This brings us full circle to fiber. There is growing evidence that elevated blood sugar levels, rising obesity, and rising rates of diabetes may not arise only from consuming too much sugar and refined grains.[33,34] The lack of fiber might be just as important.[35] Simple carbohydrates in nature are normally packaged part and parcel with fiber which naturally prevents the rise in blood sugar levels.[36]  

In the stomach, some fibers (e.g. beta glucan) form a gel that traps sugar and slows its release to the small intestine.[37] In the small intestine, some fibers (e.g. beta glucan) can decrease the transporters in the cells and gaps between the cells to decrease sugar absorption.[38,39] That’s a good thing! In the colon, some fibers (e.g. resistant starch and beta glucan) are transformed by the microbiome into butyrate, which stimulates the colon cells to make the GLP-1 hormone.[40,41] GLP-1 signals fullness and regulates appetite as discussed in Part 1, but also regulates how much insulin is being produced by the pancreas and how well muscles take up sugar to use it for energy.[42]

So to summarize it is important to limit sugar, but it’s also important to increase fiber. The fiber-to-carbohydrate ratio has been touted by some as a better metric of how much sugar and fiber to consume and has been associated with lower blood glucose and weight.[43] Aiming for foods or food combos that have a ratio of greater than 10 grams of sugar to 1 gram of fiber is great and a ratio of 5 grams of sugar to 1 gram of fiber might be golden. Low FODMAP fiber supplements can also be helpful in reaching the recommended 30g of fiber a day. At the end of the day, consider fiber is a powerful and empowering complement to other blood sugar centric strategies for weight loss! (See blog on fiber) 

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Christopher Damman, Associate Professor of Gastroenterology, School of Medicine, University of Washington. Editor-in-Chief of Gut Bites MD.

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