March 20, 2020
The Levels team is always scouring scientific research to determine effective strategies to improve our metabolic fitness. We take “metabolic fitness” to mean our ability to keep average and fasting glucose levels in an optimal range, minimize post-meal glucose spikes, optimize insulin sensitivity, and to exhibit flexibility in utilizing different energy sources -- including stored fat and glucose -- for fuel.
The beauty of striving for improved metabolic fitness is that it is in our control. Where we fall along the spectrum of metabolic health has largely to do with our dietary and lifestyle choices, and as such, is dependent on making consistent, well-informed decisions.
In order to improve our metabolic fitness, we have to first track our glucose levels, and then we have to know how to modify them. Fortunately, continuous glucose monitoring (CGM) lets us track how specific foods and lifestyle behaviors are impacting glucose levels in real time, helping us expand our metabolic awareness. With our personal data in hand, we can then turn to the scientific literature to provide us guidance in reaching our goals.
This article will explain 12 strategies that have been shown to positively impact glucose levels, and that members of the Levels team have utilized to improve our own metabolic fitness.
Note: This is purely educational content. Always talk with your healthcare practitioner before starting any new dietary or lifestyle intervention.
“Time restricted feeding” means consuming all your day’s worth of calories in a relatively short window, and abstaining from eating the rest of the time. One study in overweight, non-diabetic individuals showed that even engaging in time restricted feeding for just 4 days can lower fasting glucose, fasting insulin, and mean glucose levels significantly.
In this study, metabolic parameters were measured in two different conditions: in the first condition (time restricted feeding group), participants ate all calories between 8am-2pm (a 6 hour "feeding window") for 4 days. In the second condition (control group), the meals were spaced out between 8am-8pm (12 hour "feeding window") for 4 days. At the end of 4 days, the time restricted feeding intervention led to significantly lower fasting glucose, fasting insulin, and mean glucose.
What’s more, the time restricted feeding group demonstrated lower post-meal glucose peaks, despite eating the same meals as the control group!
Timing of food intake matters: our bodies are naturally more insulin resistant at night, so the exact same food eaten in the morning tends to have much less of a glucose spike than that food eaten at night. One study showed that eating food later in the evening will cause a significant increase in both insulin and glucose levels compared with eating the same meal consumed in the morning. In this study, evening meals were at 8:30pm and morning meals were at 9:30am.
Looking to minimize glucose spikes? Eating earlier in the day may be a good bet. Food eaten at night, especially if it is a “high glycemic index” meal, appears to cause an exaggerated glycemic response.
Bottom line: Based on scientific studies, a strategy to improve metabolic fitness includes eating each day during a ~6-8 hour window, and finishing last food intake no later than mid-afternoon. Eating later in the evening negatively affects glucose levels more than eating the same foods earlier in the day.
Intermittent fasting means restricting food intake for longer periods of time, usually for 24 hours or more. A recent small case report in three individuals with type 2 diabetes showed that intermittent fasting could meaningfully reverse diabetes in as little as 7 months. These participants did 24 hour fasts, 3-4 times per week.
What does this look like in practice? It means that participants ate dinner, and then didn’t eat any calories until dinner the next day. All 3 participants were able to regain enough insulin sensitivity to get off their high doses of insulin medication within 3 weeks of starting their fasting regiments. One participant, who initially was taking 80 units of insulin daily, was able to discontinue all insulin injections after just 5 days of fasting!
Intermittent fasting is thought to increase expression of genes, hormonal pathways, and cellular physiology that improve metabolic fitness and insulin sensitivity. Levels co-founder Josh has done extended fasts before, and has seen his average glucose gently trend down into the optimal range and remain there with only 2-3% variation for days at a time, his body turning to fat-burning pathways (and production of ketones) to keep him energized.
Bottom line: 24 hour fasts can improve insulin sensitivity. For practical purposes, this means eating breakfast one morning, and then not eating calories again until the next morning.
This one is simple and highly effective: if you’re trying to optimize your glucose, then don’t eat food that was made in a factory, comes in a package of any kind, or doesn’t look at least somewhat like its original form in the wild. Top of the list to eliminate? Added sugars of any kind, refined grains (ie, anything made with refined flour), and refined fruits (ie, juice).
If a nutritional label has a non-zero value next to “Added sugars,” it’s not an ideal choice for optimizing metabolic fitness. Even innocuous items like protein bars can have as much as 15 or more grams of “added sugar.” Additionally, products labeled “low-sugar” or ”low glycemic” can still be full of added sugars. The truth is, we don’t need any added sugars in our diet for health, and certainly not if we are striving for improved metabolic fitness. These added sugars can be in obvious foods like soda and candy bars, but can also be in less obvious foods like ketchup, salad dressing, and pasta sauces.
Naturally occurring sugars in their whole food form, like sugars in fresh fruit, are generally going to have less of an effect on glucose levels, as they will be surrounded by unprocessed fibers and other nutrients, making them slower to be digested.
Generally speaking, any food in its unrefined form will cause less of a glucose spike. In studies that have compared eating the same caloric amount of whole grains (least processed), coarse flour (more processed), and fine flour (most processed), they have found a linear increase in glucose and insulin elevation as the grain becomes more processed.
If you want to get your glucose into a more optimal level, stick to unrefined whole foods known to cause minimal glucose spikes in the average person. Of course, CGM will allow you to know exactly how you’ll respond to specific foods, but good choices for foods that are unlikely to cause a big spike in most people are those that are <40 on the standard glycemic index scale. These include whole food forms of: beans, tofu, chickpeas, green leafy vegetables (spinach, lettuce, collards, kale, chard), eggs, blueberries, blackberries, garlic, onions, mushrooms, zucchini, asparagus, broccoli, cabbage, cauliflower, celery, cucumber, peppers, avocados, fish, lean red meat, chicken, oils, olives, chia seeds, and apple cider vinegar.
Additionally, it is thought that the phytochemicals and antioxidants that exist in unrefined versions of plant foods can enhance the cellular processes that lead to optimal glucose regulation, particularly polyphenols.
Bottom line: Consuming unrefined, low glycemic foods will likely lead to lower glucose spikes, and improved metabolic health over time. CGM allows you to see exactly how a particular food and portion size affects your glucose response. Vegetables and low glycemic fruits also contain polyphenols which may improve glucose regulation, and can be helpful to include.
In insulin resistant individuals, high amounts of fiber are associated with lower post-meal glucose levels, insulin levels, and lower glycemic variability (glycemic variability refers to up-and-down swings in glucose). In a study of 18 individuals, those who ate ~51 grams of fiber per day had better glucose-related metrics than those who had an identical amount of calories per day, but only ~15 grams of fiber. The fiber sources in this study included legumes, 2 servings of vegetables and 2 servings of fruits per day, and whole grains. Other sources of fiber include seeds (flax, chia, others), all types of beans, and nuts.
Bottom line: High fiber diets appear to improve glycemic control in diabetic individuals. Without being vigilant, it’s easy to not get enough fiber in the diet. To get ~50 grams of fiber per day, it requires making an effort to include fiber sources (including beans, nuts, seeds, vegetables, fruits, or whole grains) at every meal.
“Preloading” meals with fat or protein can minimize the quick absorption of glucose into the bloodstream.
In one study, consumption of 23 grams of protein and 17 grams of fat 25-30 minutes before carbohydrate ingestion significantly decreased post-meal glucose elevation in nondiabetic individuals and those with insulin resistance.
Similarly, eating fat alone in conjunction with a carbohydrate load will decrease the post-meal glucose spike. Research shows that eating 3 ounces of almonds with a meal of white bread leads to significantly lower post-meal glucose spikes than when white bread is eaten alone. Similar trends were seen when participants were served 1 and 2 ounces of almonds, but the biggest effects were seen with 3 ounces of almonds (~40g of fat).
Bottom line: Eating carbohydrates alone is likely to spike glucose more than if the carbohydrates are eaten with fat and/or protein.
Vinegar is known to have a glucose lowering effect when taken before or with a meal. One study showed that when about 1 ounce of white vinegar is consumed with a carbohydrate rich meal, post-meal glucose spikes and insulin levels are significantly lower. In addition, vinegar increases satiety ratings of a meal! In this particular study, the carbohydrate used was white bread containing 50 grams of carbohydrates.
Bottom line: Taking in a small amount of vinegar along with a carb-rich meal appears to generate a lower post-meal glucose spike.
Exercise of pretty much any form (including mild aerobic activity, moderate aerobic activity, high intensity interval training, and resistance training) improves metabolic fitness and glucose control. One study showed that a single session of exercise at even a mild intensity (50% or 65% VO2 max) has the ability to significantly increase insulin sensitivity the very next day.
Additionally, a large body of research shows that moderate aerobic exercise for 30+ minutes, 3+ times per week, for 8+ weeks improves insulin resistance and glycemic control, including fasting glucose levels.
Similarly, high intensity training actually improves both fasting glucose and insulin sensitivity in as little as two weeks.
It is also important to optimize timing of exercise for glucose control. Long story short: short bursts of activity multiple times per day lowers glucose more than one big chunk of exercise once a day. How so?
One study compared 3 exercise regimens that all added up to 60 minutes of exercise per day:
1. 20 minutes of jogging 30 minutes before meals (repeated 3 times a day)
2. 20 minutes of jogging 30 minutes after meals (repeated 3 times a day)
3. Multiple short bursts of exercise throughout the day (3 minutes of jogging every 30 minutes, repeated 20 times a day)
It was found that the short but regular bursts of exercise done by group 3 were most effective in reducing post-meal glucose spikes. Some of us on the Levels team opt for being active in short bursts throughout the day to keep glucose down, rather than doing one big chunk of exercise before or after a meal.
The same effects hold true for walking. Another study compared two walking regimens, both of which added up to 30 minutes per day. The two groups consisted of:
1. Participants doing a single 30 minute block of walking once per day
2. Participants doing 1 minute and 40 seconds of walking every 30 minutes throughout waking hours
This study showed that the frequent, short walks in scenario 2 were significantly more effective at reducing post-meal glucose peaks and insulin levels than a single longer period of walking, despite both groups doing the same number of total walking minutes per day.
Bottom line: Exercise of any type helps with glucose control and metabolic fitness. Short, frequent bursts of exercise seem to be more effective than longer isolated chunks of exercise. Try to be active all throughout the day!
Sleep is absolutely critical to glucose regulation and metabolic fitness. Restricting sleep to 4 hours per night for just 5 days has been shown to significantly decrease glycemic control and metabolic fitness. In one study, this amount of sleep deprivation led to a higher glucose response to specific foods, and a 40% lower rate of glucose clearance from the blood during a glucose tolerance test, as compared with participants who are able to get 12 hours of sleep per night.
In fact, partial sleep deprivation generates metabolic responses in otherwise healthy individuals that appear to be similar to people with clinically impaired glucose tolerance. Just a short stint of sleep deprivation can send the body into pathologic metabolic states. Luckily, this may be reversible in as little as 2 days by improving sleep duration.
Bottom line: We need good sleep (7-9 hours per night for most adults) to have proper glucose regulation. No matter how good a diet is, sleep still plays a key role in metabolic function.
Stress raises glucose levels, and if we want optimal metabolic fitness, we have to take ownership over managing the stress in our lives.
Studies have shown that there is a significant correlation between perceived work-related stress and increased levels of circulating glucose.
Additionally, in mice, acute psychological stress (meaning getting repeatedly shocked on the foot and then having to escape a cage) leads to acute insulin resistance (cells become “numb” to the effect of insulin), with significantly reduced clearance of glucose after a glucose load.
Fortunately, stress management techniques can be effective at reducing glucose levels. In a study of insulin resistant individuals (patients with type 2 diabetes), those who engaged in a program of 20 minutes of daily diaphragmatic breathing exercises showed reduced fasting blood glucose and post-meal glucose levels at the 9th week of the study as compared to those who did not do the breathing intervention.
Additionally, 6 months of twice weekly meditation practice in individuals with heart disease has been shown to result in a significant decrease in fasting blood sugar, post-meal blood sugar, and hemoglobin a1c.
Bottom line: Stress of any kind can negatively impact glucose levels. Self-care in many forms, including meditation and deep breathing, can promote improved glycemic control and metabolic fitness.
Ingestion of large amounts of saturated fat has been shown to acutely decrease whole body insulin sensitivity by about 25%. Saturated fats include fatty cuts of beef, pork, lamb, dark chicken meat, poultry skin, dairy foods (milk, butter, cheese), tropical oils like coconut and palm, and margarine. To optimize insulin sensitivity, emphasizing unsaturated fats like nuts, seeds, olives and olive oil, avocado, fish, soybeans, and tofu appears to be a better bet.
Bottom line: We try not to overdo it on saturated fat, as it seems to be associated with lower insulin sensitivity. Favoring unsaturated fats is likely better for metabolic function.
Interestingly, multiple studies have shown that drinking a large amount of water with a meal will cause an increase in the peak of glucose and insulin after a meal, likely because the fluid load speeds entry of food into the small intestines for rapid glucose absorption. With that said, good hydration overall is an important part of metabolic health, so we never skimp on water, we just try to be smart about when we drink it in relation to our meals.
Bottom line: We try spacing out large amounts of liquids an hour or two from meals.
Compounds in cinnamon have been found to improve insulin signaling and glycemic control through a number of potential mechanisms. This is true even in individuals who are non-diabetics: A study of 41 healthy adults assessed whether glucose levels were improved with taking 1 gram, 3 grams, or 6 grams of cinnamon per day for 40 days. The participants were instructed to mix their daily dose of cinnamon powder with apple and milk and consume it. At the end of the 40 day study, those individuals taking any of the doses of cinnamon (1, 3, or 6 grams) all had a statistically significant drop in the post-meal glucose levels after a standardized meal. This effect was largest for the group taking 6 grams cinnamon, who’s post-meal glucose levels dropped from a mean of 105 mg/dL to 92 mg/dL. Additionally, those individuals taking 6 grams of cinnamon had reduced pre-meal glucose levels, indicating that their baseline glucose during the day was lower.
Bottom line: Based on the research, cinnamon may be a helpful adjunct in the quest towards improved metabolic fitness. Given that high post-meal glucose spikes are associated with worse health outcomes, cinnamon may be an effective way to blunt these surges.
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