Wed, Dec-17-14, 03:50
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Plan: P:E/DDF
Stats: 225/150/169
BF:45%/28%/25%
Progress: 134%
Location: NC
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Going back to the topic of feeding the gut microbiome, and needing more soluable fiber than a VLC diet provides in order to improve blood glucose regulation, Franziska has a new post on the topic.
http://www.lowcarbdietitian.com/blo...loss-and-beyond
Quote:
Over the past few months, several women have contacted me expressing frustration at being unable to lose weight despite strictly following a LCHF diet. When I ask whether they're including high-fiber plants like brussels sprouts, berries, nuts, and dark chocolate, the response is typically, "I avoid those because they're so high in carbs. I limit my carbs to less than 20 grams total." This is the trend I've noticed lately in the low-carb community: the belief that limiting vegetables and other high-fiber plants in an attempt to keep carbohydrate intake at an absolute minimum (sometimes as low as 10 grams of total carbohydrates per day) long term is the key to losing weight.
Soluble Fiber's Role in Improving Blood Glucose Regulation
A few weeks ago, Martina from the KetoDiet App website wrote an excellent blog post about counting net carbs vs. total carbs for those following a carbohydrate-restricted lifestyle. In the article, she correctly states that insoluble fiber passes through your system without being absorbed, so it should be subtracted from the total carbohydrate count. In addition, Martina explains that, unlike insoluble fiber, soluble fiber does not pass through the colon but rather is fermented into short-chain fatty acids (SCFAs) by our gut bacteria.
The principal SCFAs are acetate, butyrate, and propionate. Of these, propionate is the only one that can be converted into glucose via gluconeogenesis (1). But would this have any significant effect on postmeal blood glucose given that most fiber is insoluble and only 15-40% of any soluble fiber will be converted to propionate (2)? Take brussels sprouts, for instance, one of the few foods that contains more soluble than insoluble fiber. A 1-cup serving has about 4 grams of soluble fiber. Less than 2 grams will be converted into propionate, and the amount of glucose produced from it via hepatic gluconeogenesis would be quite small, so serum blood glucose levels wouldn't be affected much.
More importantly, as Martina pointed out, De Vadder, et al, recently reported the results of a study on mice suggesting that SCFAs promote intestinal gluconeogenesis (IGN), with propionate acting as substrate and butyrate promoting the expression of genes necessary to induce this process. Compared with control mice fed their normal diet, mice who were fed diets enriched with SCFAs and fructo-oligosaccharides (FOS) experienced lower fasting serum blood glucose levels, improved glucose tolerance, and a significant reduction in the enzyme responsible for hepatic gluconeogenesis (3). Essentially, propionate is converted to glucose and used within the intestine, decreasing the amount of glucose produced by the liver, resulting in the above-mentioned benefits. Yes, this was an animal study, but it provides an intriguing explanation for the improvement in blood glucose levels seen in human studies examining the role of dietary fiber (4, 5).
Blood glucose response to fiber-rich food may differ among some people with Type 1 diabetes, whose blood glucose levels can reportedly rise as a result of higher food volume in the stomach or other stimuli, regardless of digestible carbohydrate intake. Dr. Bernstein and others with T1 have suggested such a response (what he calls The Chinese restaurant effect), but I know of no studies confirming this and would appreciate references if anyone has them.
Health Benefits of Fiber and SCFAs
We've known about the benefits of fiber on colon health for decades. Although it's believed these are due in part to insoluble fiber's ability to reduce intestinal transit time so potentially carcinogenic substances in our food spend as little time as possible in our GI tract, more recent research suggests that fiber's chemoprotective effects may be due primarily to the effects of one of the SCFAs, butyrate (6,7), which provides energy and nourishment for the cells of the colon.
In addition, higher fiber intakes may reduce levels of C-reactive protein (CRP) and other inflammatory markers, improve our immune response, and protect the gut from harmful microorganisms that can make us ill (8). In essence, fiber's fermentation to SCFAs helps keep our gut well nourished and working the way it should.
Increasing High-Fiber Carbohydrate Intake May Be Helpful for Weight Loss
Let's go back to restricting intake to less than 20 grams of total carbohydrates in order to lose weight. When carbohydrate intake is this low, there's a limited number of foods that can be eaten: meat, cheese, fish, eggs, butter, cream, coconut oil, olive oil, and small amounts of greens and other very-low-carb vegetables. Yes, carbohydrate intake may be well below 20 grams of total carbs daily, but depending on portions consumed, calorie/energy intake may be too high to promote weight loss. A serving of bullet-proof coffee contains 440 calories, zero carbs, zero protein, and zero fiber.
Aside from fiber's beneficial effects on overall health outlined above, consuming at least a moderate amount of fiber can facilitate weight loss, and both insoluble and soluble fiber can be helpful in this regard.
Insoluble fiber passes through the body without being absorbed. It adds volume to meals, but zero calories and zero carbohydrates. In fact, you could almost say that insoluble fiber provides negative calories, in that it may lower the amount of energy derived from fat and protein when all three are consumed at a meal (9). Most foods are higher in insoluble than soluble fiber, with a few exceptions (Please refer to Martina's fiber chart in the blog post linked to above).
Soluble fiber does contribute calories/energy to the body, but no carbohydrates. The chief benefits provided by soluble fiber are due to its fermentation to the SCFAs acetate, butyrate, and propionate, which have been shown to promote satiety, reduce intake, and and decrease body fat (3,10-11).
Carbohydrate and Fiber: What's Optimal?
Like carbohydrates, fiber is another substance where across-the-board recommendations can't be made, but I think it's best to aim for at least 20 grams daily, with 1/3 or more from soluble fiber. If you're limiting yourself to less than 20 grams of total carbohydrate, the maximum amount of fiber you can possibly get is 18 grams, and that's only if the carbs come from foods that are more than 90% fiber, such as chia seeds, flaxseed, or avocado. Generally speaking, those who consume diets containing less than 20 grams of total carbohydrate end up with 10 or fewer grams of fiber. Some people reportedly consume less than 5 grams on a consistent basis.
The goal of carbohydrate restriction is to keep blood glucose and insulin levels low, and this can be accomplished without reducing carbs to near-zero levels. I consume around 30-45 grams of fiber daily, and my net carb intake is around 35-50 grams, so my fiber to nonfiber carb ratio is roughly 1:1. This works well for me, but some people do better with 20-30 grams of fiber and slightly lower net carb intake. People with certain GI disorders* may require restriction of certain types and amount of fiber.
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Last edited by JEY100 : Wed, Dec-17-14 at 04:01.
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