The Physician’s Guide to Fitness is a multi-part series that covers the steps you need in order to get in shape and improve your health.   Read parts 1, 2 & 3 here.


Step 5: Nutrition

Disclaimer: The following advice applies to individuals without metabolic or autoimmune disease that requires special dietary restrictions. Please consult your physician before incorporating the guideline.


With steps 1-4 your mind and spirit are primed to make actual changes in your body. At any given moment when an individual decides to become more physically fit, he or she will fall under two categories. Either you have too much extra body fat or you are pretty lean but you’re lacking muscle tone. For now lets focus on fat loss (cutting in fitness lingo) which is a vital piece of your fitness knowledge even if you don’t have much body fat to lose since you’ll have to know how to do it eventually.


The reason I am emphasizing cutting before muscle building is because becoming lean is relatively much easier and much more rewarding when you fit into slimmer clothes and have more chiseled jaw line. By leaning down whatever muscles you already have will actually show so you can track your muscle growth in the next phase when you are actually building them in size or toning them if you’re a woman. Keeping the fat on and jumping into muscle gain will put you in the proverbial no-man’s land where you are neither slim nor fit at all.




Comparing the above two iconic cinematic warriors can help clarify this concept. Russell Crowe in Gladiator had ample muscle mass but he wasn’t very visually impressive because he also had plenty of fat covering his muscles which made him just plain bulky.


Michael Fassbender in 300 actually had much less muscle mass but he was far more athletic and had a domineering on-screen presence because he had very little body fat that emphasized his existing muscle tone (he is considered cut in fitness lingo).


BMI Scale


You will have to gauge your current body fat range by eyeballing it. For men the ideal “fit” look would be between 11-12 %. For women it is 21-23%. Later on as you lean down and gain more muscle mass (that includes women), the “athletic” look you will shoot for will be in the 8-10% for men and 18-20% for women. For this cutting phase I recommend men to cut down until they are 10% body fat and women to shoot for 20% body fat to prepare for muscle building.


There is a baseline metric called the basal metabolic rate (BMR) that is largely determined by the energy expenditure of your lean body mass including muscles, bones, and internal organs. This number can vary depending on your levels of non-exercise activity, exercise activity, stress, and genetics. Trying to factor in all of these elements to get the precise level of the daily caloric use can get pretty tedious and the impact of such calculation will not be too significant.


Body mass loss or gain is predicated on an incredibly simple scientific principle. If you eat more than you can burn via BMR, you will gain fat which is called being in caloric surplus. If you eat less than your BMR, it is called being in caloric deficit. The reason many people fail to effectively lose fat is because they lack proper guideline to practice caloric deficit in a long-term schedule and return to BMR in a gradual change.


I will provide the guideline that helped me cut 25 lbs of body fat in 18 months and maintain the lean physique for the following 6 months before I started building muscle size. There are a few more concepts you must understand before you can start taking control of your eating habits.


Individual BMR will vary depending on your height. The taller the person, the bigger lean body mass which will burn more energy even just by sitting around all day. So you must take an honest measurement of your height and determine what your maintenance calorie is. This is your daily intake calorie that will neither gain nor lose any body mass.


BMR Scale


A 5’8” male such as myself can consume up to 2200 calories a day of any type of food (including ice cream and French fries) to stay the same. A 6’4” male can consume up to 3000 calories a day without any change.


At any given time the human body is in 2 metabolic states: fed state and fasting state. During fed state after eating food, your body has had an influx of nutrients in the form of macromolecules such as carbohydrates, protein, and fat. These macromolecules (macros for short fitness lingo) will break down into smaller forms of glucose, amino acids, and smaller fat which will lead to lipogenesis with the help of insulin by leading the nutrients into fat cells. In fasting state the body requires energy to provide calorie level of your BMR so glycogen stored in the liver and muscles start to break apart. Glycogenolysis is followed by lipolysis of the fat cells.





During the course of the day your body’s metabolic profile will look something like this.




What we want is to have the quantitative area of the blue graph exceed the green on a daily basis. When this is done over a long period of time the consistent lipolysis will lead to a visible reduction of fat deposit throughout your body. The problem is carrying on such deficit in a long-term period ranging from months to years takes professional, social, and psychological challenges. We’re not living in a bubble eating perfectly balanced meals just for the sole purpose of looking good. A modern day human being lives a rather chaotic life that is continuously being swayed by entropy in the forms of work, school, culture, fatigue, stress, happy hours, comfort food craves, and just about any number of random confounding factors that can creep up.


The diet modality that has been supremely effective in my life and in the fitness circle is called intermittent fasting (IF for short). Intermittent fasting puts a curfew on the feeding window (a time period where the green graph is allowed) and enforces a strict fasting window to maximize the big blue graph you see on the far left.


In addition this exercise will start building your habit for documenting your metrics on nutrition intake, weight lifted on your reps, and body measurements during your transformations. In essence you are starting a patient chart on yourself.


  • Calculate your caloric deficit – If you have a lot of fat to lose, some drastic deficit would work well for the first 4-6 weeks. I would recommend eating no lower than 1500 for men and 1200 for women since you’ll still have to go to school or work and actually use your brain and body to live your life. If you are exercising at least 3 times a week than the deficit does not have to be too low. Take your BMR and reduce it by 20-25%. My BMR is 2200 so I would cut with a daily intake of 1800.


  • Practice calorie counting for about 1-2 weeks: use an app to familiarize yourself with calorie counting to get an idea of what a 400-600 calorie meal looks like. Generally it’s best to eat the same breakfast, lunch, and dinner respectively most of the week. You can even eat the leaner menus at fast food restaurants which is much easier since the calories are listed or you can calculate them online. I lost my first 15 lbs with McDonalds grilled chicken menus for 9 months. Afterwards you’ll develop an ability to eyeball calories.


  • 12:12 split (beginner IF – 12 hours of fasting and 12 hours of eating) In the morning pick a time when you normally eat breakfast (literally breaking fast) and start counting 12 hours. You will have your 3 or whatever number of meals you have within that 12 hours. During my rotations I woke up very early to workout and usually ate at 6 am. How you plan your individual meal in terms of quantity and timing is up to you. The best method that works for me is to have a medium breakfast in all 3 macros (carbs, protein, fat) with coffee, eat a medium size lunch higher in veggies and protein, and back-loaded the bulk of my calories at dinner with protein, fat, and most of my daily carbs so that I could last 12 hours of fasting starting 6 pm. If I needed snacks in between meals I would have protein bars or shakes that had about 200-300 calories at a time. With 8 hours of sleep the only waking hours of non-eating was 4 hours in the evening that mostly consisted of reading and studying. During your fast you cannot eat or drink anything that has calories. Make your own split whether it is from 7 am to 7 pm or 9 am to 9 pm.


  • 16:8 split (advanced IF – 16 hours of fasting and 8 hours of eating) – Once you have gotten used to the 12:12 split and if you’re able to tolerate long hours of fasting, you can increase the fasting window to 16 hours. I usually fasted between 6 pm and 10 am the next day. The beauty of this method is you are essentially eating 2 meals during the 8 hour window. Your stomach can take only so much food at a given time so even if you didn’t accurately count calories, the routine will automatically create a deficit big enough to induce significant fat loss. You can arrange the hours however you wish. If you can fast until noon and have dinner a little later that works. If you need to eat early in the morning and be done with food by late afternoon that’s fine too. You can choose to eat a big meal first and a medium meal later. However I find having a big dinner is much more effective because you can feel satiated at the end of the day and help you endure the fast.


  • Refeed Days – When such deficit is practiced long term, there are certain drawbacks that predictably fail diets every year. The body’s metabolism will start to slow down as overall body fat reduces. The body burns less fat over time. The hormone leptin, a hormone that provides satiety or sensation of fullness, will reduce and the individual will have a hard time enduring craves. For women this is much worse because their leptin level fluctuates more rapidly. Psychologically the person will start to feel weary of eating fewer calories day in and day out. So during the week, men should have caloric deficit for 6 days and have a reefed day by eating at BMR. This is will boost leptin levels back up for better satiety and dopamine for pleasure of eating more food so that you can go on for another week. On the long run this will prevent rage or binge eating from accumulated stress. This is also the perfect opportunity for a cheat meal (not a cheat day) that can include that extra 400-600 calories in the form of hamburgers or ice cream. For women refeed days can be little more frequent. Female fitness coaches have attested that menstrual cycles can cause cravings so if you are having hormonal changes and feeling some hunger, having 2 refeed days 2-3 days apart can be effective. For example, men can eat in deficit Mon-Saturday and refeed on Sunday. Women can alternate 1 day refeed week schedule (Sunday) and 2 day refeed week schedule (Wednesday and Sunday) depending on what their body is telling them. Whichever day is your off day from work and can feel most comfortable for relaxed eating should be your refeed day.


  • Chew – Take a moment to engage the taste and texture to appreciate what many people around the planet lives without everyday. Chewing will slow the overall process.


  • Don’t watch anything with your meal – Mindless eating can lead to quick eating that will make your body difficult to feel satiety. Be engaged in your meal time with your friends or family and try to feel fulfillment with each swallow. Once you’re done sit back and try to feel the effects of leptin doing its work. The net result will be less intake to reach your caloric deficit. Be Zen.


  • Sleep – As I have mentioned in Step 1, everything starts and ends with sleep. A huge portion of your fasting window is taken up by 7-8 hours of sleep which makes the process much easier. Even if you somehow screwed up your calories and fasting, my advice is always get your sleep and try again the next day. If you put yourself in repeated sleep deprivation, leptin level goes down which lowers satiety and ghrelin level goes up which raises hunger sensation. Next time you miss out on sleep try to objectively measure your cravings and the amount of food you eat just to compensate for the fatigue.


With this plan you can get a feel for what work-life schedule best suits your productivity and adjust as you go along. Even if you couldn’t last 12-16 hours of fasting and had to eat a snack, it’s better to keep the same schedule because this is meant to work around your life with consistency.


Certain tips like black coffee in the morning, sparkled water in the afternoon, apple during snack time, and small amount of dark chocolate after dinner have proven to be helpful in suppressing appetite and having daily treats as rewards. Your overall stomach size will begin to shrink and fasts will become much easier.


Physiologically the body is allowed to have an opportunity to burn fat without being interrupted by insulin pumping nutrients into fat cells. Psychologically having a strict curfew on your feeding takes a lot of decision making burden out of your day which frees up your mind to focus on your academics, life projects, and pleasure activities. This is a good reflection of Step 3’s Zen mindfulness practice of letting things go once your fasting starts and leaving everything else behind you. You can trust the process that your fat cells will start to burn during your fasting hours.


Now that we have a plan on how to eat, lets talk about what to eat. IF does not emphasize omitting any food groups. Unless you are a vegetarian or vegan, you can eat just about anything. If you have a lot of fat to lose it’s smart to be a bit stricter. I highly recommend you cut down all processed carbs and grease in the form of soda, chips, pastries, and fried fast food.


1-2 drinks of alcohol is okay as long as you make room in your daily intake plan and not binge. As you lean down you will be able to eat some treats more frequently and not have a big effect starting around 12% and 22% body fat respectively for men and women. What matters is HOW MUCH YOU EAT, or how many calories. Whether it is from a cookie or a carrot, a calorie is still a calorie. Eating too much of healthy food is pointless if you’re trying to lose fat.


Low carb diet is an archaic fad that only helps towards losing glycogen and water weight for photo-shoot preparations. It does nothing for losing fat (the difference in weight vs fat). A physician is required to be moderately physical and highly cerebral for long hours so carbohydrate is incredibly important to make clinical decisions. If you’re exercising in the gym you cannot train long term without carbohydrates.


A good standard to designing your macro composition is to make sure you take in lean protein everyday and build the carbs and fat around it. Men are recommended to have 100-120 grams of protein a day and women should take 60-80 grams per day. I usually treat a fillet of lean chicken as 25 grams of protein so if I’m missing protein from lean chicken, fish, and meat I will supplement with Whey protein shake or bar to make up the missing amount. Afterwards I usually just take complex carbs by eating multigrain bread or brown rice in moderation. If you truly wish to be meticulous about your macros, try to get 40:40:20 ratio of carbs, protein, and fat respectively in your daily intake.


An important factor to reaching caloric deficit is how well you can achieve satiety. Make the salad bar your best friend. Fresh vegetables are virtually calculated to have zero calories but are very fiber rich to fill you up so eat them as much as you can. Legumes such as cashews and almonds are a healthy fat source that will improve the salad taste. Try to avoid rich creamy condiments such as ranch or thousand island and take olive oil or vinaigrette instead for flavor. Additional healthy amount of fat from avocado will boost your satiety and maintain normal hormone productions such as testosterone which is necessary for strength and lean mass production. Should you have a big bowl of salad with all the macros for dinner every night, you will be able to fast for 12 – 16 hours without any trouble.


Finally you must learn how to improvise. If your work place cafeteria happens to lack lean food, then eat a little less and make up later where you have more control. If there’s a group lunch that wasn’t in your plan just go with them and eat a little less later. If there’s a Thursday night happy hour you are attending, plan ahead and eat in more deficit starting Thursday morning and look up alcohol calorie content for a few minutes before heading out to be mindful while having fun.


For high stakes obligations such as exams and interviews, eat however you feel that will give you the best performance possible 1-2 days prior and resume your nutrition plan afterwards. 1-2 days of a deviation does not derail an entire month’s course of proper dieting. Flexibility and freedom is the ultimate fitness goal! You are not supposed to be enslaved to your food. It is not your enemy. It brings people together. Life is meant to be fun. Relax. Have a beer. It’s only less than 200 calories.


Resource: Eat Stop Eat by Brad Pilon, Anything Goes Diet by John Barban, Muscles for Life blog by Mike Mathews, Fitmole blog by Kieth Lai


Donghyun John Kim

Donghyun John Kim

DO, Founder of Doctors of Steel

John Kim is a Family Medicine Resident and founder of Doctors of Steel. John is passionate about helping medical students and physicians achieve fitness and work-life balance. Learn more at