Science Spotlight: Grant Tinsley

Grant Tinsley Circle

I simply want to use any knowledge, talents, or abilities I possess to maximally impact others in a positive way.



Grant works as an Assistant Professor at Texas Tech University. He teaches undergraduate and graduate courses in sports nutrition, skeletal muscle physiology and strength and conditioning. His major research areas are intermittent fasting, body composition assessment, dietary supplements and resistance training. He also works as a freelance writer for Authority Nutrition at Healthline.

Check out Grant’s scientific publications and articles. Grant has previously reviewed The Ketogenic Diet part 1 and How the Ketogenic Diet Affects Hunger, for Sci-Fit.

Interview with Grant

Hello, Grant. Could you give our readers a short introduction about what you do in the world of fitness and nutrition?

Yes, I’d be happy to.

Academic research is currently my main area of focus in the fitness/nutrition realm. I am finishing my second year as an Assistant Professor at Texas Tech University. My appointment has a fairly light/moderate teaching load, which frees up quite a bit of time to devote to research. I do teach 1 to 2 courses per semester.

I also do some freelance writing about nutrition, dietary supplements and exercise. Although it isn’t a large part of my career at present, I do some one-on-one fitness consulting and maintain my CSCS and CISSN credentials.

Could you tell us a bit about the research and teaching you do at Texas Tech?

Absolutely. On the research front, there are three main areas I am currently pursuing:

  1. How diets like intermittent fasting affect body composition, performance and health effects in combination with strength training.
  2. Body composition assessment methodology (i.e. evaluating the validity and reliability of different body composition tools and determining which factors affect the accuracy of body composition estimates)
  3. Evaluating dietary supplements.

In terms of teaching, I typically teach 1 to 2 courses per semester. Sports Nutrition is the main undergraduate course I teach, although I have also taught Anatomical Kinesiology and Strength & Conditioning.

I also currently teach a graduate-level Skeletal Muscle Physiology course each fall. Pending the final approval of my department’s Ph.D. program in Exercise Physiology, I start teaching some new doctoral classes in the 2018-2019 school year.

What are your main scientific fields of interest?

My main areas of interest are pretty much in line with the three areas of research I briefly mentioned earlier (i.e. intermittent fasting, body composition assessment methods and nutrition/dietary supplements).

My interest in intermittent fasting evolved out of conversations I had with my former adviser, Dr. Paul La Bounty. He was the first author on the International Society of Sports Nutrition’s 2011 position stand on meal frequency.

One of the major conclusions of this position stand was that a high meal frequency did not seem to possess the major metabolic and body composition benefits anecdotally ascribed to it.

This was fascinating to me, as I had read countless ”fitness articles” about the miraculous benefits of eating every 2 – 3 hours. If you don’t have to eat constantly to improve body composition or health, how frequently do you have to eat? Is there a lower limit? These were a couple of the questions that sparked my initial interest in intermittent fasting.

Dietary supplements also interest me for a few main reasons. First, I feel that they should be under close scrutiny since they are so popular. There is also a lot of misinformation about supplements, particularly online.

Some people take countless unnecessary supplements, while others completely write off all supplements as useless. I want to help develop this field. As it has in the past, the systematic investigation of dietary supplements will help researchers, practitioners and consumers understand which supplements may be useful, and under which circumstances.

Body composition assessment methodology makes me feel so nerdy, and I just love it. Body composition is used to describe the proportions of different components of the body, including fat, water, bone mineral, protein, etc.

Your have published studies and two reviews on intermittent fasting (IF) - What motivated you to research fasting and what were your findings?

Big-picture summary

There are many types of intermittent fasting. In general, intermittent fasting can be a viable way to reduce body fat and improve health. But, it might not necessarily be superior to other methods.

Like any dietary method, intermittent fasting will be superior to other options for some people and inferior for others. There is a distinct lack of IF research in active populations, and my collaborators and I recently published the first two studies of IF in combination with resistance training.

In my reviews of intermittent fasting, I concluded that multiple forms of intermittent fasting are viable methods (but not necessarily superior methods) to reduce body weight, fat mass and improve several CVD/metabolic disease risk factors. This has also been supported by more recent research findings.

As someone who is interested in active populations, two things caught my attention as I was reviewing the literature in this area: (1) results concerning loss of lean body mass were somewhat mixed, and it wasn’t clear if there were any differences in lean body mass retention between IF and traditional caloric restriction; (2) there were virtually no IF studies that incorporated exercise (with the one exception at the time being traditional ”cardio” in combination with alternate-day fasting in obese middle-aged adults). Even today, the vast majority of IF research has been conducted in sedentary and obese individuals.

Due to these gaps in the literature, as well as the popularity/controversy associated with IF in the active population, I knew I wanted to conduct original research in this area. I was specifically interested in time-restricted feeding (TRF; limiting all food intake to a particular window of time each day) due to the very limited human data from this form of IF and its popularity. Finally, I wanted to conduct the first intervention that incorporated resistance training in combination with IF.

Around that time, I was fortunate enough to meet Dr. Antonio Paoli at a conference, and we began discussing our mutual interest in this area. We were both conducting research on TRF plus resistance training, and this sparked a productive collaboration between us. The first two, and currently the only two, articles presenting data on IF (specifically TRF) plus resistance training were published out of this collaboration. The project I led was very much a pilot study and was conducted with very limited resources. The project led by Antonio was much more in-depth and provided answers to some of the deeper physiological questions surrounding IF. While both of these studies provided some preliminary information in this area, there is much more work to be done. We are in the process of preparing a publication reporting longer-term effects of TRF plus resistance training, and I am currently leading a study of TRF plus resistance training in women.

Lastly, the new review article I published with Ben Horne emphasized a few recent developments in IF research, including the discussion of IF in the recent Scientific Statement from the American Heart Association and the year-long trial of alternate day fasting (which essentially showed no benefit of ADF compared to traditional caloric restriction).


In 2016, you published a review on how the ketogenic diet affects lean body mass - What is your take on the diet as a whole?

My opinion on the ketogenic diet as a whole is that it can certainly be an appropriate diet for some people, but that it is probably not a sustainable long-term option for the majority of the population.

The big-picture result of our review was that lean body mass is lost during weight loss with a ketogenic diet, just like during other diets. Some studies reported greater loss of lean mass during the ketogenic diet, while a handful of others saw no difference. However, the majority of studies employed the ketogenic diet for the purpose of weight loss, without the addition of regular exercise. We also discussed the limited number of articles available at the time which combined resistance training with the ketogenic diet. The results of these were also mixed, with no clear benefit of the ketogenic diet.

If I’m allowed a brief side note: working on this ketogenic diet review article is actually what initially sparked my interest in body composition methodology. Specifically, I was concerned about the potential differences in liver or muscle glycogen stores in diet groups with varying carbohydrate content, particularly in the studies incorporating exercise. Shortly after, Rouillier et al. published an article that showed a 3-day high-carbohydrate diet can increase DXA lean body mass even though a ”real” change in lean mass couldn't occur in this very short period of time.

That is, increasing carbohydrate intake increased lean mass due to more glycogen and water stores in the body rather than due to actual increases in muscle protein or other tissue. After these developments, I led a study examining the effects of acute food and fluid consumption on DXA and BIA body composition estimates. This analysis was published in MSSE earlier in 2017.

Are there any groups of people who would get extra benefit from intermittent fasting or the ketogenic diet?

Yes, I think so. There are groups of people who could get extra benefit from any particular diet, provided that the diet in question is a feasible and sustainable way for them to move towards their health goals.

If intermittent fasting or the ketogenic diet is something that is feasible (preferably enjoyable) for you, and you find that you can make the body composition or health progress you want while following it, great for you!

Personally, I think this is more likely to occur with intermittent fasting than a ketogenic diet.

Intermittent fasting doesn’t say anything about what you eat per se, but it may be an effective way for some people to reduce their caloric intake. For some people, it is easier to follow the directions of ”don’t eat” and ”eat” to reduce energy intake rather than counting carbohydrates or calories, adhering to a list of certain ”approved” foods, etc.

Of course, intermittent fasting could be combined with any dietary approach that focuses on what you eat. During his or her ”feeding window,” someone can follow a ketogenic diet, a high-carb diet, a plant-based diet, or whatever they want.

With all that said, there are some people who would hate their life if they had to stop eating for longer than an overnight fast. If that is you, you probably shouldn’t torture yourself by trying to do IF. I think that the unique benefits of a particular eating strategy, if they truly exist, are far outweighed by the importance of feasibility and sustainability.

So, to get back to actually answering the question, the people who would get extra benefit from these dietary strategies are the people that enjoy them and find them an agreeable way to move towards their health goals.

You have done some important work regarding body composition estimation (DEXA and BIA) - What have you learned?

You worded this question well. We really can’t measure body composition, so all the techniques we use simply provide estimates. With that said, the accuracy of these estimates can vary widely. All methods have limitations, sometimes substantial limitations. When assessing people with abnormal physiques (such as bodybuilders), these limitations may be magnified.

Overall, here’s a big-picture takeaway from some of my recent research: we need strict standardization and proper data reporting.

The question of ”how can we describe what our bodies are made of?” can get more complicated than you’d think at first glance. The vast majority of research in the fitness realm does not use methods that would be considered ”criterion” or ”gold standard.” Instead, we often use methods like DXA and BIA.

I did publish some comparisons of DXA and BIA, but really both of these methods have several of their own unique limitations. This may come as a surprise to many readers, but DXA results are far from infallible.

We commonly assess physique-minded individuals who think their DXA results are gospel. This simply isn’t true. Several recent studies, including one of my own and one from Louise Burke's lab, have demonstrated that DXA lean mass estimates can be artificially increased by food, fluid and substance (e.g. creatine) ingestion. BIA is also affected by these dietary factors, but to an even greater extent.

While food and fluid intake seem to affect the lean mass estimates from DXA, they don’t affect bone or fat mass estimates as dramatically. However, most BIA devices essentially predict both fat mass and fat-free mass from the same electrical values. So, when fat-free mass increases, fat mass automatically decreases.

Both DXA and BIA also share some other important limitations, such as assuming a particular water content of fat-free mass. This is an area that I am currently investigating in my lab.


How accurate are our methods for estimating body composition? Is there a gold standard?

Many of the methods you typically see in research studies are not very accurate, particularly when small changes in body composition are being discussed. In many cases, the error of the device can exceed the supposed changes in body composition. What’s more, it is even harder to say whether a particular individual has really experienced a change in body composition, as opposed to a group. Multi-compartment models (e.g. a 4-compartment model) that include an estimate of body water are generally considered the gold standard.

Before subjects are tested, they should fast overnight. If this isn’t possible, assessments should occur earlier in the day when less food and fluid have been consumed. There are some data showing that the cumulative amount of food and fluid ingested in the day is directly related to the magnitude of errors induced in lean mass/fat-free mass estimates.

Many frequently-used methods are often not very accurate. Sometimes the problem is that the error of these techniques is larger than the actual changes seen due to some type of intervention. However, the ”accuracy” of different methods also depends on your purpose for body composition assessment. One important consideration for the fitness community is that some moderately accurate methods are acceptable for looking at group differences (i.e. the analyses performed in many research studies), but not for assessing an individual. For many methods, you would need enormous changes in an individual’s body composition to be confident that a real change occured. This has important implications for practitioners who are working individually with athletes.

Some generally respected methods (i.e. Bod Pod, underwater weighing, and even DXA) can require an individual to experience a body fat percentage change of 4 to 6% before you could be confident that a true change really occurred (here’s an article discussing these methods in athletes). If you think about a lean athlete, these magnitude of changes may be quite rare. However, these methods may be more appropriate at the group level.

Discussions about body composition assessment tools can get fairly in-depth, so I’ll do my best to summarize a few important ideas. In fact, I’ll start with the ”gold standard” question and work my way from there.

In general, the ”gold standard” for body composition estimation are multi-compartment models, particularly those that contain a body water estimate. Models with at least 6 compartments have been described, but 4-compartment models are typically used as a criterion/”gold standard” method. A traditional 4-compartment model needs estimates of body mass (i.e. scale weight), bone mineral (from DXA), body volume (from underwater weighing or air displacement plethysmography [Bod Pod]) and body water (traditionally from deuterium dilution or similar methods, but bioimpedance spectroscopy [BIS] or multi-frequency BIA are increasingly utilized). When you plug all of these components into a validated equation, you can get your fat mass estimate. This allows you to calculate lean body mass and body fat percent.

To generalize, the more you simplifty a multi-compartment model, such as the four-compartment model, the more error you potentially introduce into your estimate. For example, you could eliminate either the estimate of bone mineral or body water and have a three-compartment model. You can simplify further and use a 2-compartment model, which only needs estimates of body mass and body volume. Bod Pod and underwater weighing use this type of 2-compartment model. At an individual level, the errors in body fat percentage can be around ±4.5 – 6% for Bod Pod and around ±4 – 5% for underwater weighing, as compared to a ”gold-standard” multi-compartment model. However, at the group level, these errors can be more like 2 – 3%. There are some studies showing DXA actually performs worse. Of course, advances in equipment and software can potentially impact accuracy, and not every specific device has been examined.

The more you simplify your body composition model, the more assumptions and error are introduced in your estimates. For example, a major assumption for any body composition estimation that doesn’t involve body water measurements is that approximately 73% of fat-free mass is composed of water. Many techniques use this assumption, including DXA, Bod Pod, underwater weighing, and anthropometric equations. However, several studies have documented the fact that the proportion of fat-free mass that is made up of water varies between individuals. This is certainly true in athletes, and it ultimately affects the accuracy of body composition estimates. Some true experts in this area (like Jordan Moon) say that the only way to accurately track small changes in body composition is to use a multi-compartment method with an estimate of body water included. The existing data justify this conclusion.

Since many labs won’t use dilution techniques on a regular basis, BIA and BIS can provide estimates of body water that can be used in multi-compartment models. Although impedance devices have limitations (just like all other methods), I think they are unfairly demonized at times. There is an enormous variety of impedance devices, ranging from the cheap $50 scales you can buy at the store to $10,000+ devices which employ many (sometimes hundreds) of frequencies of electrical currents. These higher-level devices can certainly be used for good body water estimates, particularly the devices that were specifically validated against deuterium dilution. Several models have also been well-validated against full 4-compartment models for body composition estimates. I have a few of these devices in my lab, in addition to DXA, for use in multi-compartment models.

Overall, the ideal method is probably to use a 3- or 4-compartment model that includes an estimate of body water. One interesting modification of the 4-compartment model is the emergence of modified 4C models that only require a DXA scan and an estimate of body water (often from BIS). In these models, body volume is predicted from the DXA scan output. A few early papers have validated this method, and I published one article about the test-retest reliability of these models, but more information is needed (particularly in active populations).

Of course, many practitioners (and even some research labs) won’t have all the equipment necessary for these assessments. In those cases, you need to standardize and control as much as you can, and then just realize that you need to interpret body composition estimates with quite a bit of caution. As discussed, more caution is needed at the individual level as compared to larger groups.


You dropped a protein review paper in 2017 - How important is protein?

Protein is quite important! I think that many people recognize the importance of this macronutrient, but the discussion of ”how much is enough?” is worth having in the fitness community in particular.

There have been a number of nice discussions on this point recently, including the ISSN’s recent position stand on protein. As almost anyone who looks at the protein literature will probably agree, the RDA is too low for many populations, including the active and the elderly. The 1.4 – 2.0 g/kg range recommended in the ISSN position stand was nearly identical to what we recommended in our protein article.

There are certainly benefits of higher protein diets, although you can reach a point at which there may not be any additional benefits of continuing to increase intake. With that said, I personally recommend erring on the higher side of the recommended intake range unless there is a specific reason not to. There is individual variability in protein needs for achieving a positive muscle protein balance, as demonstrated by recent data. Since any given individual won’t know where their particular requirement truly falls, it may be safest to aim for the higher end of the recommended range.

In terms of the protein review article, I have to give a shoutout to the person who did the real work on this project – Elisa Morales. Elisa is a good friend of mine who is finishing up her Ph.D. at Baylor University. She is brilliant and was the one who was responsible for the design and execution of that project.

If you had to choose your top 3 scientific research papers, which ones would it be and why?

My favorite paper is typically the one I am currently working on. I just love writing, and I’m always looking forward to the next paper. I am not great about stopping and reflecting, but I think three of my favorite research papers are:

1: Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males.

Reason: This was just a really cool study, and I was very happy to be a part of it. This was one of the first projects where I got to work with Antonio. It’s also rewarding to be a part of projects people are interested in. I think this article has almost 100,000 accesses between the journal website and Researchgate in the year and a half since it was published (plus who knows how many within PubMed).

2: Effects of intermittent fasting on body composition and clinical health markers in humans.

Reason: This article was just a documentation of my initial exploration of the intermittent fasting literature while I was in my Ph.D. program. I learned a lot through writing this article, and I just focused on writing the type of article I was looking for (but couldn’t find in the existing literature). I think this also helped me form an idea of some of the subsequent original research I wanted to conduct in this area.

3: Impact of Acute Dietary Manipulations on DXA and BIA Body Composition Estimates.

Reason: This was my first data collection focused on body composition assessment methodology, and the collection and analysis were just a lot of fun. This project began a line of research for me that I plan to continue indefinitely. I really enjoy that fact that you can answer multiple important methodological questions from a single data collection if you set up the experiment appropriately.

What do you want to achieve with your work in the future?

I simply want to use any knowledge, talents, or abilities I possess to maximally impact others in a positive way. For now, this will largely be through my role as a professor. I think the academic environment is somewhere I see myself staying for quite a while. Educators have a unique role in impacting the students we work with, both in and out of the classroom.

Being a researcher in the realm of nutrition and fitness is really rewarding because there are so many well-informed members of the general population who are interested in the results of this research. It is also exciting to connect with researchers and practitioners from all over the world thanks to conferences and online interactions. I don’t know which route(s) my career will ultimately take, but I’m open to considering any opportunities that arise in the future.

I think science is an amazing tool that allows us to gradually understand more about the incredible world we live in. I’m thankful to have the desire and means to contribute to the collective body of knowledge. On that note, I have to mention that I am very much at the dawn of my career. I have only been conducting research for a few short years, and I am eagerly looking forward to many years of growth as a scientist and educator in nutrition and fitness.

Which research topic do you think needs more attention?

I think there are a number of important questions that need to be answered within my areas of interest.

In terms of intermittent fasting research, I think we need some highly-controlled metabolic ward studies to fully clarify if there are any true physiological benefits of IF independent of calorie restriction (and if so, what the magnitude of these effects are). The existing studies, including the ones I have been a part of, have largely been unable to exert the level of dietary control that would be necessary to adequately answer this question.

On the practical side of IF, I would like to see more research identifying predictors for those who may experience success (or failure) with an IF program. We have recently published an interesting article about subjective responses (hunger, desire to eat, prospective food consumption, etc.) during acute fasting, as well as subsequent energy intake. I think the idea of collecting data on individuals during ”test fasts” to see if they fit the profile of someone who may find success (or not) with IF is interesting.

There are a lot of topics within body composition assessment that need to continue to be investigated too. Overall, I am just interested in the continual refinement of both laboratory and field methods for body composition estimation in a variety of populations. We need to continue to pursue the optimal combination of feasibility and accuracy in our methods.

Do you want to give any shoutouts?

Yes, I do. First and foremost, my wife Tessa is an absolute hero. Her support through the years has greatly contributed to my ability to pursue the work I love.

As I mentioned earlier, Paul La Bounty was the person who sparked my interest in IF and initially advised me during my doctoral program. When he relocated to another university, Pete Grandjean at Baylor was kind enough to take me on as a student (while still allowing me to pursue my own research interests).

Working with Antonio Paoli over the past couple years has been great, and he continually produces a lot of interesting work related to nutrition and resistance training. In body composition methodology research, Jordan Moon is someone who has produced a ton of great work. I rely heavily on a lot of his papers, and he has been very willing to answer questions and assist me in this area. I also have a great group of colleagues in my department at Texas Tech.

Lastly, the writings of Francis Collins (Director of the NIH and a leader of the Human Genome Project), and Timothy Keller have been influential in my understanding of science as a discipline and how it fits into human existence, religion, and the universe.

There are a lot of other collaborators, peers and friends who are deserving of a shout-out, but I will truncate my list here so it doesn’t get obnoxiously long.

Grant's Research

Study Link Year Type
Intermittent Fasting and Cardiovascular Disease: Current Evidence and Unresolved Questions Link 2018
Time-Restricted Feeding in Young Men Performing Resistance Training Link 2017 RCT
Effects of Eight Weeks of Time-restricted Feeding on Basal Metabolism, Maximal Strength, Body Composition, Inflammation, and Cardiovascular Risk Factors in Resistance-trained Males Abstract

Full-text PDF

2016 RCT
Comparison of High-protein, Intermittent-Fasting Low-Calorie Diet and Heart Healthy Diet on Vascular Health of the Obese Abstract

Full-text PDF

Effects of intermittent fasting on body composition and clinical health markers in humans Link 2015 Review
Intermittent Fasting Programs and Their Effects on Body Composition: Implications for Weight-Restricted Sports Abstract

Full-text PDF

2015 Review

Grant's Articles