By Spencer Medick, Pitching Coordinator
At Driveline, we’re known for objectively measuring performance criteria, and making training recommendations based on that information. With an increase in wearable biometric tracking devices available to the public, we decided to test out Levels to get quantitative insights on nutrition and compare that to scientific literature to evaluate how nutrition can affect performance.
This will be a comprehensive literature review on nutrition, primarily around blood glucose, as well as a product review of the Levels app, and continuous glucose monitors (CGMs) as a whole.
If you’re not interested in taking a deep dive, but want the basic, science-backed 411 on nutrition, we’ll start there.
There are general heuristics:
- Eat whole foods
- Eat mixed meals (protein, carbs, & fats)
- Consume adequate daily calories based on needs
But everyone has a slightly different response to food types, meals, timing, and quantity. If optimizing health or peak performance is your goal, it could be wise to find out what works best for you.
- Lift weights and get jacked—more muscle increases insulin sensitivity and helps you deal with larger amounts of glucose.
- The Glycemic Index is less than useless.
- Since athletes stick to a pretty regimented schedule, a 3-day test with a glucometer might be a more efficient solution than obtaining a CGM through a doctor.
Nutrition Is Individual
Ever wonder why almost every diet seems to have tribalistic followers who swear by it, while others say it’s complete garbage? Well, that’s because people have various responses to different meal types, timing, and even individual foods—though hardly anyone eats a single food in complete isolation. A well-known study by Zeevi, et. al. revealed a high degree of interpersonal variability in postprandial response between identical meals. That’s a fancy way of saying that the same meal activated different cascades of internal responses and pathways in different people.
Rather than demonizing foods or following recent health crazes, find out what your body can handle, and what it can’t. But before we get into that, let’s look at what factors can affect responses to food, because food is fuel.
Exercise and Muscle Mass
Ever been jealous of a friend who’s jacked and can eat whatever they want? Well, despite what you may have been told, it’s not entirely genetics. While it’s true that you can’t out-train a crap diet, having more muscle mass significantly increases both insulin sensitivity—your body’s ability to deal with a large bout of glucose consumption—and the amount of energy you’ll need to fuel your muscles. In a study by Andersen, et. al., when controlling for amount of body mass, more muscle was correlated with more glucose dissipating before entering the bloodstream.
After resistance training, insulin sensitivity remained elevated up to 48 hours post-session. There also was a major difference between resistance training and aerobic training in terms of its ability to affect insulin sensitivity. So, while aerobic training is vitally important for cardiovascular and respiratory function, along with the functioning of a number of metabolic pathways, the key to true metabolic health lies in resistance training.
Why is insulin so important?
In non-scientific terms, insulin keeps you from caramelizing your red blood cells, organs, nerves, and other vital tissues. Have you ever heated a pan, added onions, and then watched as the onions change color and generate a sweeter flavor? Well, that caramelization process is heat activating the release of sugar, which breaks down the structure of the molecules to make glucose more accessible. When you consistently run high blood glucose levels (diabetes) or have large spikes in blood glucose (insulin resistance), this process is basically taking place within your bloodstream and everything else within reach. This is the core reason why a sedentary lifestyle and hyper-nutrition create a whole host of other health issues.
So, in short, the more muscle on your body, the more carbs you can handle. Not a bad thing right? Get jacked. It’s good for your health and your performance.
The glycemic index has been used for quite some time now to “grade” and make recommendations on food quality, specifically carbohydrate sources. This should cease to exist…preferably yesterday, and for a multitude of reasons. First, again, nobody eats food in isolation. Even if you’re eating sugar in the form of a cookie, there are fats involved that will slow digestion and glycemic response. Enjoy that cookie with a glass of whole milk? Same story, which muddies the water further. Second, the utility of the glycemic index has been entirely debunked by numerous research studies:
“Low GI/GL diets do not lead to significantly more weight loss than higher GI/GL diets over the moderate term in overweight or obese people. To address the sources of uncertainty, there is a need for larger, longer, higher quality trials.” – Braunstein et. al.
“There is currently no evidence available regarding the effect of low GI diets on cardiovascular disease events. Moreover, there is currently no convincing evidence that low GI diets have a clear beneficial effect on blood lipids or blood pressure parameters.” – Clar et. al.
“We did not find any significant effect of dietary glycemic index or glycemic load on serum concentrations of inflammatory cytokines, including hs-CRP, leptin, IL-6, and TNF-α in adults.” – Milajerdi et. al.
If you go off any sort of glycemic index to judge the quality of the foods you’re eating, you can just go ahead and stop. It’s a terrible predictor of food quality.
Sugar is not the devil
So why go through all this just to debunk glycemic index? Well, because sugar shouldn’t be seen as the devil. In fact, it could be your best friend. If you’re an active college or professional athlete, how are you expected to eat enough calories during the day when you have 4 hour practices, plus weight training, potentially classes, and other life events that prohibit you from eating frequently and getting enough calories?
Additionally, if you’re trying to get enough calories in during the day using sweet potatoes as your carb source…well good luck with that. Sometimes you need to “dirty up the diet” to hit your caloric needs, whether that’s cereal, sandwiches, hell, even peanut butter Pop-Tarts if it calls for it. Just make sure your blood glucose doesn’t spike above 140 mg/dL after a meal.
So, how does one get an internal picture of how their body responds to meals? Well there’s a few options:
A glucometer is your standard finger prick test and is accessible over the counter and for relatively cheap; however, most people are not too keen on repeatedly jabbing their finger throughout the day. A glucometer is a seen as the gold standard because It measures the blood directly—measuring blood glucose more accurately.
Standard test with glucometer:
- Stick yourself and take glucose reading at the beginning of a meal.
- Measure every 30 min for 2 hours postprandially.
- If you reach your initial “baseline” you’re done.
You should be able to return to your baseline within 2 hours of a meal, and sometimes within an hour. If not, you may want to speak to a primary care doctor.
Continuous Glucose Monitor
Much more convenient to use, a CGM is a hardly noticeable device that sits on the back of your arm and is surprisingly painless. It measures the interstitial fluid, leaving about a 15 minute delay between readings and actual blood glucose levels. On top of that, you need a doctor’s prescription to get your hands on one. Each sensor lasts about 14 days, and can give you daily insights and trends throughout the day. However, because many athletes operate on similar routines, including their diet, it may be overkill and redundant to repeatedly use a CGM for more than a month.
Testing with a CGM is way easier than with a glucometer:
- Scan your CGM with your phone periodically throughout the day.
- That’s it. You can analyze your trends and log meals within the app to see your response.
Now that you know how to measure your blood glucose, as well as the tools that are available to you, how do you know what you’re looking at?
Generally speaking, the general consensus is that “resting” blood glucose levels between 80-90 mg/dL are optimal for health and longevity. However, stress, food intake, and exercise can all affect these throughout the day, so there will be some natural variability. The Levels app makes it easy to understand. Their proprietary algorithm gives you a Daily Metabolic Score, as well as a Zone Review for each meal (as long as it’s tracked).
If you are tracking your glucose levels manually through a glucometer, you’ll want to keep total blood glucose excursions under 50 mg/dL from your baseline. So, if your baseline is at 90 mg/dL, following a meal you’ll want to keep your blood glucose levels at least below 140 mg/dL. If you’re using a CGM, since it measures interstitial fluid rather than the blood directly, it’ll be glucose excursions closer to 30 mg/dL from baseline.
Avoiding jumps in blood glucose
That said, regardless of what device you’re using, don’t fall into the fragility mindset trap that anything over those guidelines is “bad” or “poor metabolic health”. A general rule of thumb is while you want to avoid high and low jumps in blood glucose, an excursion outside these ranges is not the end of the world. As long as you avoid large swings and stay within the 80-120 mg/dL range for most of the day, you’re likely in good metabolic health.
The human body is an amazing system with lots of backstops and processes built in to keep you in homeostatic balance, from insulin kicking in to help dissipate high blood sugars, to your liver kickstarting gluconeogenesis if you go hypoglycemic (low blood sugar) in order to have readily available energy.
Speaking of hypoglycemic, it’s important to mention that you may want to avoid low blood sugar as well as high blood sugar. There is some supportive evidence that shows that hypoglycemia is associated with cardiovascular complications. While you may not have low blood glucose levels so often, it is important to note that hypoglycemia could also be induced by the swings in your blood sugar. What matters more is the size of the swing, rather than the levels themselves. Sometimes bigger spikes can lead to lower lows, so it’s something to look out for and monitor. Subjectively, this can potentially be associated with that crash or lethargic feeling after a meal.
Tying this all in, Levels has built an app to help make tracking and awareness of metabolic health more accessible to the general public. Typically, a CGM is only available through a doctor’s prescription and only given to those with diabetes; however, Levels has gathered a network of independent doctors who, depending on your state, can write you a prescription after you fill out a short questionnaire. Currently, since Levels is still in beta-testing, you can sign up for the waitlist here.
Levels is a great tool for users of any background who are interested in optimizing health and performance.
For the Beginner:
- 1-10 score for metabolic response to meals and snacks
- Daily score based on responses to meals, stress, and activity
- Daily, weekly, and monthly reports both emailed and accessible within the app to objectively measure diet and lifestyle choices and how they affect research-backed, long term health markers
For the Intermediate:
- Food challenges and logs within the app to experiment and fine tune individual responses to food, both objectively with blood glucose levels and subjectively
- Plan individualized meal template, timing, and exercise based on glucose responses throughout the day
For the Advanced:
- Maximize health and performance through variable meals with low and higher glycemic response
- Tailor exactly which foods or mixed meals you personally respond to best
- Plan workout types and time of day based on metabolic response
The app itself is extremely intuitive, making tracking and understanding your blood glucose swings easy, even for the absolute novice. With a score system between 1-100, the daily scores are extremely easy to understand. On top of that, each meal, when logged, can give you a metabolic score based on your blood sugar swings and the time it takes to return to baseline.
The morning after, you will receive a daily report emailed to you, breaking down your day’s performance and meal scores if you logged them, including your average glucose level, variability, and time in optimal range, among others. All this information can be found within the Levels app, but it is readily accessible through daily emailed reports.
If you’re a little more familiar with blood glucose, or have read this blog, then you can view your blood glucose within the Levels app and monitor it throughout the day, rather than relying solely on the metabolic scores.
So, where is the benefit of wearing a CGM and using the Levels app? Well, there is a lot of education built into the app itself. Articles are categorized from Athletic Performance, to Mood, Focus, and Energy.
We at Driveline believe a more educated athlete is a better athlete, and clearly the team at Levels believes in the same. From educational reading resources to guided personal experimentation, the Levels app is like having your own personal nutrition coach at your fingertips.
As always, you get out what you put in. The resources exist within the app to give you the tools and information you need to get started, regardless of your goals or your current experience level.
From a research perspective, there is a massive value in having CGMs in the hands of larger populations, both metabolically fit and unfit. Most research in the blood glucose realm has been done on more diabetic or unfit populations. Having a larger dataset, paired with even just basic activity levels (Levels can connect with Apple Health and automatically log your workouts) and food logging, we can develop much greater insights on exercise, nutrition, and how our choices may affect long term health. The more data from more diverse populations, the deeper the insights we may be able to draw down the road—even if that means fewer “absolutes” when it comes to training, nutrition, etc.
Most of the current drawbacks with Levels are with the hardware itself. Usually it takes the CGM about 24 hours to calibrate, since it measures interstitial fluid, meaning you may get some inaccurate and more volatile readings in your first day or two with the sensor. Don’t check it too often at first. The same thing is true towards the end of the sensor’s lifespan. On about Day 13 or 14, a few users reported that the sensor tended to drop low and deliver glucose readings lower than normal, affecting scores in the Levels app. You’ll truly get about 11-12 high quality days of readings, but there are a few days in there that you may not draw significant insights from.
Getting started with Levels is $399, which gets you 2 Freestyle Libre sensors, access to the app, and a welcome kit to help you get started. This lasts you about 28 days, and you are then charged $199 per month for a monthly subscription. Most of these costs are currently to cover the hardware (CGM). Having a dietician or nutritionist typically runs you between $50-$100 per hour, so this is roughly priced in the same ballpark as a weekly meeting with a dietician. However, you will have access 24/7.
You can also pause and resume your subscription. So, if you find yourself in a good routine and don’t necessarily need a CGM, you can pause your subscription, then if you have a significant lifestyle change or just decide you want to switch things up, you can easily resume your subscription service and get yourself back on track.
Given Driveline’s core mission of finding more objective measures of performance and training, Levels’ new-to-market biometric tracking app can be the next step in measuring and planning for individual performance. Whether you’re a high-level athlete or a general fitness enthusiast, or just trying to lose weight and take control of your health and longevity, there is tremendous value in Levels.
Its objective measurements are useful, as are the built-in educational and coaching experience to lead you on a self-guided journey. Having accurate data about your metabolic health can also help dispel some sacred cows in the diet and “health” industry. For example, the belief that eating before bed is bad for you, that breakfast is the most important meal of the day, etc. It allows you to find out how your body actually responds to foods, timing, exercise, stress, and a large number of other factors.
Personally, I work out in the mornings and tend to eat a lighter breakfast, as I am more sensitive to glucose spikes earlier in the day. Later in the evening, when I am winding down after a long day, my body is parasympathetic and primed to digest and deal with meals, limiting my postprandial glucose excursions.
As we gather more nutrition data and pair it with performance data, we can gain further insights on how to properly fuel athletes for performance on an individual level.
If you’re interested in getting set up with Levels, you can follow this partner link to skip their 100k+ person waitlist, sign up and take the next available slot.