Weight Loss 101: What’s Actually Happening Inside You? [Infographic]

Megan Meyer, PhD
by Megan Meyer, PhD
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Weight Loss 101: What’s Actually Happening Inside You? [Infographic]

You know the math when it comes to losing weight: Eat smarter and exercise. What you don’t need is fad diets or get-thin-quick schemes. It’s all about data — and if you’re logging in MyFitnessPal, a little scientific knowledge helps you understand what’s going on inside you. That’s what we’re here to provide: a comprehensive look at what happens in your body when you’re looking to lose weight.

It all starts with calories, the basic unit in foods and beverages that provides your body with energy. All calories are the same: 150 calories from a cookie or Greek yogurt is still 150 units the body converts to energy. But how many you can handle is unique to your body: Your calorie budget depends on a variety of factors, including your physical-activity levels, muscle density and genetics. Now to the science …

About the Author

Megan Meyer, PhD
Megan Meyer, PhD

Megan is a lover of all things science, food, and fitness. A scientist by training (go Tar Heels!), Dr. Meyer has found that being able to communicate the science is just as important as understanding the science. Dr. Meyer has a BS in Biology from Loyola University Maryland as well as a PhD in Microbiology and Immunology from the University of North Carolina at Chapel Hill and is a regular contributor to sites like US News & World Report and The Huffington Post. In her spare time, she enjoys whipping up fun recipes in the kitchen, exploring new trails, and spending quality time with loved ones. You can follow her on Twitter.


47 responses to “Weight Loss 101: What’s Actually Happening Inside You? [Infographic]”

  1. Avatar Ghetto Counselor says:

    Hi Doctor Meyer, What’s the current science on eating back calories from exercise saying? This seems a topic of confusion on many blogs and other discussion groups and since exercise is seemingly always part of a well rounded diet it would seem useful to understand how to balance it in the thinking on diets. To give you some sense of the landscape I’m thinking of I’m wondering about both the after work trip to the gym with a HIIT style spin for 30 minutes, say 300 calories as well as the weekend warrior 1500 or more calorie 75 mile 4 hour road ride. Those are two very different scenarios and I suspect the philosophy to handle them is different as well. Appreciate your thoughts!

  2. Avatar Waleed Ansari says:

    I appreciate what you have written based on your knowledge. But just considering calories and not the levels of insulin in the body and it’s resistance, tells me that you’re either unaware or simply don’t understand what’s really happening inside our bodies.

    • Avatar Lytrigian says:

      Or, she was presenting a general overview without getting too deep into the details of the biochemistry.

      Besides, just considering calories works.

    • Avatar Cindi Seal says:

      I agree… I think her assertion that “all calories are the same” is misleading. The metabolic effects of weight loss are a huge component that should not be swept under the rug. Simple calorie deficit based on simple BMR calculations will NOT (generally) result in continued weight loss in the long run, especially for those who have a significant amount of weight to lose. You must factor in the considerable slowing of the metabolism and try to counteract it, else starve.

      • Avatar He-Man says:

        It is true that reductions in BMR from losing body weight can counteract some part of the deficit, but it has never been shown to cancel it completely. This is why you never see fat POWs or fat anorexics.

        Some people do have what is known as a thrifty metabolism, which is when given the same diet and exercise program, the person will experience different results, due to differences in how their body responds to being in a deficit. Some people’s bodies are extremely adaptive, and will not lose nearly as much as a less thrifty person with the same weight and height.

        The same correlates to weight or fat gain. Some people respond to overeating differently than others. Some people’s bodies are more efficient at storing fat than others. As a result, given an experiment where people were asked to overfeed the same percentage of calories over a period of time, some people gained lots of body fat, and some people gained hardly any.

        That’s why the 3,500 calorie per pound rule is a myth because it does not consider adaptations of that person’s physiology to being in a calorie deficit.

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        • Avatar Cindi Seal says:

          Great clarification, and well said! Any chance you have a reference/citation for the study? Would love to read it to better my understanding. Thanks!

          • Avatar Ronald Jones says:

            Try Dr. Jason Fung, The Obesity Code. See his YouTube videos also.

          • Avatar Cindi Seal says:

            Thanks for the tip! He has some interesting ideas.

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    • Avatar He-Man says:

      I think you have been somewhat mislead. High levels of insulin alone do not explain insulin resistance. Insulin’s job is to regulate the uptake of nutrients by the body’s cells by telling them to open up.

      Without insulin, you would not survive. Food ingested causes the pancreas to release insulin into the bloodstream. As nutrients are being absorbed into the cells, insulin levels drop until all the nutrients are absorbed and insulin remains at the baseline level. Every time you eat food, this occurs, regardless of whether your perceived insulin levels are low or not.

      Insulin has a role to play in fat storage, but so do many other hormones. One of insulin’s main functions is to protect against high levels of blood glucose by stimulating glucagon. During this process, insulin inhibits the breakdown of fat cells and stimulates the formation of new ones. While this may sound scary, it’s not– the body is consistently forming and burning fat cells for energy.

      In periods were food intake is not happening, the body’s insulin levels drop to baseline, and the body is mainly burning fat for energy, but in periods of food ingestion, the body stores ingested food as fat and goes through a process of both forming and burning new fat cells. The 24 hour cycle of nutrient intake will decide whether the body will store excess energy from glucose reserves as fat, or to burn it through a process of oxidation, which can only be triggered by a deficit in ATP ( a calorie deficit).

      In the case of insulin resistance, the problems occur when due to many reasons, the receptors of the cells are unable to receive the signals from insulin to allow the nutrients to flow through. As a result, insulin is unable to do its job by signaling glucagon to break down excess glucose in the blood. As a result, the pancreas releases more insulin to respond to the excess glucose, but the glucose in the blood keeps building up, as insulin is unable to shuffle the nutrients in the cell to support a healthy blood sugar. As a result, insulin resistance occurs.

      The biggest predictor of Type 2 diabetes, by the way, is body fat gain. There are examples of many cultures that have extremely high carbohydrate intake, yet have the fewest incidences of Type 2 diabetes and cardiovascular disease.

      • Avatar Cindi says:

        I am a 61 year old female. I have been involved with the fitness industry for over 40 years. I have been diagnosed with being insulin resistant. I do cardio for 45 to 90 minutes 6x per week. Weight training 30 to 45 minutes 3 to 4x per week. I am also a massage therapist with an average of 30 hours per week of deep tissue massage .I eat a low carb diet. I eat approximately 1200 to 1400 total calories per day of mostly protein and vegetables and
        I can’t lose weight . I have been to see numerous nutrionionists and no one can solve it. My cholesterol is also high. I want to lose 20 pounds

        • Avatar Henry Aarvold says:

          Hi Cindi, try adding more saturated fats to your diet. Add organic butter to your veg. Go for more fatty grass fed/pastured meat like lamb, pork and beef rather than just lean protein like chicken. You’ll be surprised by the effect this will have on your health and weight loss. Don’t count the calories, just listen to your body and eat when only when hungry.

        • Avatar Olivia says:

          Too much cardio can be an obstacle to lose weight. The key is builfing muscle as miscle requires more energy to run. More muscle = more cals you’ll naturally burn. Low carb, high protein diets have been shown to create resistance in the body in the long yerm and make it more and more difficult to lose weight over time, and that would explain the high cholesterol too, as I assume these protein cone from animals’ bodies mainly.
          Have you tried a high carb, low fat diet? Sustainable, great for fat loss and most healthy. That did (is doing it for me) 🙂

        • Avatar Shepard says:

          Eat less

        • Avatar rosa says:

          Hey Cindi,
          Check out this book by Diane Kress, RD, CDE, titled The Metabolism Miracle
          It has helped hundreds of people also myself with issues of weight loss . I have gone on many low carb diets only to regain the lost weight, this book will give you great insight into what can be done to lose weight for good.

        • Avatar joe says:

          Different methods work for different people. I’ve had some success with intermittent fasting and HIIT (interval training); try switching out the cardio for interval training, and take 2 days off instead of 1. Also, have a low protein/high carb day once per week. Add soluble fiber to help with cholesterol (supplement with psyllium, inulin, chia seed, flax seed, and glucomannan throughout the week). I also take Niacin, fenugreek, and aged garlic extract to help. For weight training, are you doing mostly compound exercises (squats, deadlifts, lunges, chest and military press), and increasing the weight amount over time? Best wishes to you!

        • Avatar Debbie says:

          I don’t think a low-carb diet is balanced. I eat 40% carbs, 30% fat and 30% protein. My carbs are complex carbs, whole grains, sweet potatoes, veggies, fruit… also carbs found in Greek yogurt. etc. I strength train and now use the Interval setting on the stationary bike. I also swim. I’m 62 years old with arthritic knees and have had two ortho surgeries in a year’s time. I hit a weight loss plateau. I upped the intensity of my cardio, went to Interval training on the bike, and got a food scale. It worked. I’ve lost about 93 pounds. My blood test results were terrible in 2015. High cholesterol, I was pre-diabetic, high blood sugar… Two months ago, my doctor said my recent blood tests results were as good as a 14-year-old’s. I thought he was kidding.

          He wasn’t.

      • Avatar Zoe says:

        Hey He-man I think you need to check you facts on one detail here. The body generally isn’t forming New fat cells it’s filling and emptying existing ones. This is one of the reasons it is so hard to keep weight off. As the fat cells remain in the body after weight loss, waiting for any chance to refill.

  3. Avatar Nikki Walker says:

    “All calories are the same,” gahhh I feel like you were hired by the sugar industry to write this post so the readers start counting calories again, instead of reading what’s actually being put into our food.

    • Avatar Julia Elizabeth Cooper says:

      This is a blog post written on a website owned by by a company who is in the business of counting calories. Whether or not they’re all the same, it is likely a biased article. Take with a grain of salt.

    • Avatar Nick Fergadis Giannakopoulos says:

      You do realize MyFitnessPal’s main function is calorie-counting, don’t you?

    • Avatar Kelli says:

      The source of calories has different reactions on your body. Consuming carbs creates a completely different reaction during digestion in your body then consuming protein or fats. Google glycemic index.

      • Avatar Debbie says:

        I agree. However, I use glycemic load rather than glycemic index. It’s more accurate and it’s how I lowered my A1C from 6.1 (pre-diabetic) to a stellar 5.0 (normal is 4.8 – 5.6).

    • Avatar M Blair Weng says:

      I agree. I think people need to do both – watch calories and look closely at what’s in the food.

    • Avatar Katina says:

      I totally agree. The quality of the calories matter greatly!! To say a calorie is a calorie is idiotic.

      • Avatar ITdude says:

        No, a calorie IS a calorie.. it’s simply a unit of measure of energy. You’re postulating that a watt is not a watt, or not all kilograms are the same as other kilograms. It makes no sense. The quality of the FOOD does matter, yes… but that is different. The chemical composition of what we eat effects nutrition in our bodies quite differently, which is what i think you mean to say.

  4. Avatar Ronald Jones says:

    Doctor, respectfully, please review the findings of Dr. Jason Fung. See book The Obesity Code, and the many YouTube videos by Dr. Fung. A calorie is not a calorie, and the “eat less, move more” or “caloric reduction” approach does NOT work in the long run, and everyone knows it. They all gain the weight back. It’s not as simple as you’ve explained it and if you don’t educate yourself you’ll continue to do a disservice to your clients.

    • Avatar jack says:

      An energy deficit has worked for me, and I do use this app religiously. I’m 72 and within ten pounds of my high school weight with a normal bmi. My understanding is the national weight control contains information on this matter. Men who do an hour of exercise per day and stick to 2000 calories effectively control weight over time.

      The likes of Gary Taubes haven’t repealed the laws of physics. The Doc is correct, at least in my experience.

  5. Avatar Gabriel Nguyen says:

    Not all calories are there same. Having someone on a low fat diet vs a low sugar diet having the same calories and exercise will give very different results. The moment she said all calories are the same made me suspicious.

    • Avatar Nick Fergadis Giannakopoulos says:

      Energy is energy, regardless from where it’s coming from. Sure, if we are talking long term, too much sugar and carbs will slow your metabolism and cause all sorts of issues, but in the short term, if you’re eating below your maintenance, let’s say 1200kcal/day, you will lose weight whether you’re eating chicken breasts or donuts.

  6. Avatar Rabih zeineddine says:

    Straight and easy we need no more than this simple and straight forward information, i loved it.

  7. Avatar Rona says:

    I agree with Ms. Megan. All calories are equal. Meaning even if that 150 calories come from “healthy food” like yogurt, boiled egg, wheat bread etc STILL it is still SAME and/ or EXACT calories coming from 150 calories of so-called “unhealthy” food like soda, junk food etc.

    • Avatar M Blair Weng says:

      Uh… no. The effects of 500 calories from an avacado and 500 calories from a bag of cheetos and a coke are totally different – for obvious reasons.

      • Avatar ITdude says:

        From an energy perspective, they are the same. Nutritionally, you are correct, their effects are different. But in terms of only body weight gained or lost, not so much.

        • Avatar M Blair Weng says:

          Yes, of course, technically from an “energy” perspective they are the
          same… however from a practical standpoint, i still believe it’s important to state that using the
          “calories are calories” mindset and eating 2K calories of
          fat/sugar/carb laden foods vs eating 2K of healthier (even slightly
          more), natural foods could land someone in a very dangerously unhealthy
          position regardless of equal amounts of energy used.

  8. Great info! Luckily I found your blog and I’ve saved as a favorite for later!

  9. Avatar Yasmine Mavrakis, RD says:

    The AMDR’s for fat and protein shown in the first diagram are inaccurate. The AMDR for protein is 10-35% and ft is 20-35%

  10. Avatar Floridajan says:

    All calories may be same.But calories from some foods with high fiber and good fat keep you full so you don’t feel hungry and go for junk foods. Calories with good nutrition also helps. It is the combination of calorie control and proper foods that do not spike your insulin.

  11. Avatar Mark John says:

    Very nice article. Our body requires fuel to aerobic exercise, and high energy food is the source of that fuel. That’s why when we start to workout we report feeling hungrier. If one want to lose weight fast, then this could be very Helpful. Keep it up

  12. Avatar Maria says:

    I think Your calorie budget depends on a variety of factors, including your physical-activity levels, muscle density and genetics.

  13. Avatar Debbie says:

    Very disappointing article with very little detail. Actually, I prefer the Mediterranean diet, which is 40% carbs, 30% fat and 30% protein. The body does not handle all calories the same; weight loss is much more complex than calories in and calories out. There’s also the psychological aspect as well to be considered. Kick sugar and you’ll find it much easier to get the weight off and keep it off. I could go on and on about the subject, but I’ve lost 93 lbs. and I’ve added quite a bit of muscle by eating a protein at every meal and snack, eschewing processed foods, quitting all sodas, kicking added sugar, drinking at least 84 oz of water daily, exercising regularly (strength training and cardio) and trying to hit my macro and micro goals.

  14. Avatar beauty4ashes says:

    This is an amazing article!

  15. Very good and easy to understand infographic. Well done, Ms. Megan!

  16. Does author try to say by those pictures that 50kg woman and 120kg bodybuilder man will both store 100g of glycogen in muscles? Seriously? Is it overall storage or per hour of consumption, or what? How people could know? Article should be to inform, not to give riddles. Why not put numbers in percentage of stored glycogen, instead of exact numbers, if we are all different?
    Like the other time, when other author has written on this website: “Go for this exercises with high intensity for 3min over 160bpm heart rate” – what a bull*it. To one 160 is endurance effort and to another may be anaerobic (this should be set in heart rate zones, not exact numbers) as we all are different within this one too.

    This website is so unfaithful. Is should help people but seems like is about to put some in trouble and misunderstanding. And I know, writing is difficult, I’ve been there. Sometime the hardest thing, except good research, is to write all about things, not omitting things we think are obvious (because those are not obvious to everyone), and not omitting things we has been thinking of, but forgotten to include in article. Other great thing, is to give an article to someone else, so he/she can check it or just read it, before publishing, as another person will always have a fresh look.

    Do all calories are equal? I’m not sure, but there is a difference in vitamins and minerals included. When 500g of avocado – as someone said – has a lot of healthy fats and some vitamins and minerals, then 500g of crisps will have a lot of worst quality fat and no minerals or vitamins. The choice is mine/yours/his/her… The choice is ours what we eat and where we go with that. To better life, or hospital sooner or later. The most difficult choice – I think – is to find good quality food as we get more and more processed food in stores now and even fruit and veges are not that healthy as ages ago.

    Every time you go for a diet or training plan, check it from different sources as one may be always right or wrong. I’m sorry if I did some mistakes, as English isn’t my first language. Have a good life 🙂

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