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Medical How do calories cause weight gain?

  1. Dec 8, 2011 #1
    It may superficially sound like a stupid question with a simple answer, but let me explain in more depth.

    Calories are units of energy, as you probably know, and grams are the the weight of the food. So calories are not directly related to the weight of a food. Foods range in the amount of calories per gram. So the meat of my question is basically this: if you eat the same weight of food, but foods with higher calories why do you start gaining weight? How or why does the energy cause weight gain?

    This is a possible solution I can think of: the extra calories somehow end up retaining more weight of the food than the otherwise would if you had consumed lower calorie foods.

    As an extra thought experiment related to this, imagine a "super seed" of 3,000 calories but only a weight of 1 gram. How could calories cause weight gain then? Obviously this is impossible, but it's just a thought experiment to view an extreme form of the question.

    Thanks for anyone who replies!
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  3. Dec 8, 2011 #2


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    Calories are a unit of energy, true, but kCal (kiloCalories) - which is what food is measured in - is the chemistry that contains usable energy in the form of chemical bonds in proteins, carbs, fats, etc.

    When the body absorbs food that is high in kCalories, it can use those nutrients to build muscle and tissue, increasing weight. If a body absorbs more nutrients than it needs, it has a way of storing them for later use. High kCalorie foods are more likely to be stored, resulting in fat deposition and thus weight gain.

    Low kCalorie, high mass foods (for example, fibre) are more readily passed out of the body, so they do not add to weight.

    In the case of your super seed:

    A 3000 calorie 1g seed might have the entire 1g retained (and no, not more than 1 g). It is all useful nutrients that the body incorporates.
    A 100 calorie 1g seed would have a small fraction of that 1g retained - only that which is useful fuel or micronutrients. It is probably mostly fibre.
    Last edited: Dec 8, 2011
  4. Dec 8, 2011 #3


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    For the way excess calories are stored see / search :
    Triglyceride Synthesis
  5. Dec 8, 2011 #4
    I'm an engineering student and have only taken 2 chemistry classes. It's hard to follow all the terminology used to explain triglyceride synthesis.

    I know this will sound a bit imprudent, but my question literally boils down to this: "If you eat the same weight of food, but higher calories, do you poop out less weight?"
    Last edited by a moderator: Dec 9, 2011
  6. Dec 9, 2011 #5

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    Almost all of your body weight is water.
    You need energy (carbs and fats) and a little building material (proteins) to build cells, but the cells mostly consist of water.

    So the weight of the food is not so relevant, it's mostly the amount of energy (calories) in it that dictate the weight gain.
    A typical method to avoid weight gain, is to eat food with lots of fiber in it.
    Fiber contains no nutrition at all and is simply expelled by the body again, although it does have a beneficial effect on your digestive systems.
    Last edited: Dec 9, 2011
  7. Dec 9, 2011 #6


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    Metabolic Pathways are a complex subject of Biochemistry

    Triglycerides or lipids , stored fat, are esters that are formed from glycerol ( a 3 Carbon
    alcohol and 3 long chain fatty acids . Both of which can be synthesized from carbohydrates

    Do a google search for Ester bond formation.

    Then look at : The formation of ester bonds in the synthesis of lipids.
    Last edited by a moderator: Dec 9, 2011
  8. Dec 9, 2011 #7
    Dislcaimer: this is going to be a very simplistic answer, decades of research and whole books are written about this subject. So if you want a very rigorous answer, go find those books/papers.

    Its not a mechanical issue where your body actually stores the mass of the food that you eat. All the food you eat will be digested into its constituent parts. The energy obtained from this digestion is then used to create other molecules that are necessary. For instance, if your cells need to make a specific protein they obtain the energy to do so by using eg glycogen stored in the cell to make ATP (glycolysis->krebs cycle->electron transport chain->ATP Sythase for some key words to search later) but that glycogen was made and stored from the food that you have eaten which provided the energy and constituent parts to do so.

    Thing is glycogen and other carbs are not the most efficient storage form of energy because they contain ~4kcals/gram while fats contain ~9kcals/gram. And this is what makes you fat. Constantly intaking a surplus of calories shifts your metabolic processes to take that energy and synthesize triglycerides (fats) which are a very efficient way to store large amounts of energy. These fats tend to be stored in specialized cells called adipocytes. The more 'stuff' you put into adipocytes, the larger they get. The larger your adipocytes become, the larger you 'gut' becomes. So; constant caloric surplus -> need storage -> use energy to make molecules which store lots of energy per unit mass -> have a storage depot for these molecules to get them when necessary(ie times of caloric deficit).

    A calorie is a calorie, though lots of people in the diet and fitness industry like to argue this fact. In the end though a calorie is a calorie.

    What you are most interested in is something called nutrient/caloric density and something that you must take into account is satiety. This is a very complex subject but I'll give you a quick rundown.

    Satiety is the 'fullness' feeling that tells you when you are fed. One of the signals your brain uses to assess fullness is the volume of food in your stomach. So lets take the two extreme cases: Lettuce and Peanuts. Peanuts are a very calorie dense food, they contain lots of calories in a relatively small amount of food. If memory serves a cup of peanuts is on the order of 103 kcalories. Lettuce is the other other end of the spectrum, a cup of lettuce will have maybe tens of kcalories. Therefore you can eat a truck load of lettuce, till your literally full to bursting, but you will only have taken in maybe a couple of hundred kcalories. Less than the one measly little cup of peanuts, which might hold you over for a couple of hours until your hungry again.

    This is why satiety and nutrient and/or calorie density are very important concepts. Lots of obesity research is being done now into satiation, and how a lot of those mechanisms are screwed up in the obese and how we can go about aiding the obese/overweight to lose weight without feeling like death all the time.
  9. Dec 9, 2011 #8


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    You body will incorporate more of the fuel-containing nutrients that are in the higher calorie food.

    Bulky food that contains fewer calories has a higher amount of bulk that is essentially passed through.

    That's is a very simplistic answer, but yes.

    There are important caveats that can't be ignored. As [strike]Yanick[/strike] I_Like_Serena points out for example, most of your body weight is water. And your diet will affect how much water you retain. Many "diets" that promise to lose 10 or 20 pounds in just a couple of weeks are simply diuretics that cause you to drop water ballast.

    So you can see that it is quite possible (in theory) to gain and lose weight independent of the weight of the food you consume. (We take for granted the water we consume, since it has no calories, no nutritive value, and yet we must constantly take it in to survive.)
    Last edited: Dec 9, 2011
  10. Dec 9, 2011 #9
    Okay I have a much better idea of what's going on now, even though it's very superficial it's a better start none the less.

    Thanks to all who replied.
  11. Dec 9, 2011 #10

    I like Serena

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    Uhh... :uhh:
  12. Dec 9, 2011 #11


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    It's just that the two of you look so much alike! :wink:
  13. Dec 9, 2011 #12
    Ask any bodybuilder trying to move up a weightclass ( If they're moving up a weight class they need to come in at the top of it to win. So your looking at a good 15 to 20 LB gain in lean mass) how much time they spend in the bathroom. I assure you its quite a bit.
  14. Dec 9, 2011 #13


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    D'oh! :blushing:


    (Wow. 11 hours later I can still edit.)
  15. Dec 9, 2011 #14
    I agree. Feinman and Fine's papers were used by some to claim otherwise:

    Thermodynamics of weight loss diets

    But here is a summary of the research suggesting that Feinman's and Fine's arguments are not warranted:

    Is a calorie a calorie?

  16. Apr 10, 2012 #15
    Calories between 2700 to 3000 are the causes of weight gain. If you eat more calories and burn less calories then it is the causes of weight gain. Do properly exercise for 30 mints daily and other activities like swimming, running, jugging, walk etc. Use fresh fruits and green foods items helps to in weight management. It change body figure and life style.
  17. Apr 11, 2012 #16
    The calories amount doesn't matter in weight gain only if you are burning the calories regularly with some workout plan.Also try to consume less then 2500 calories daily.Because if you'll take more than that then you should have to do heavier workout plan for burning the calories.
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