Human Limits

Exploring performance and health with Michael J. Joyner, M.D.

Photo of Michael J. Joyner, M.D.

What About Diet?

My recent focus on physical activity and obesity leads to an important question.  How much of the big increase in obesity rates seen in the U.S. over the last 30 or so years is due to what we eat?  Like some of my earlier posts on physical activity and obesity this one is going to be data intensive.


We are eating more!

The U.S. Department of Agriculture (USDA) reports interesting statistics on what people are eating in the U.S.  The figure below shows trends in calories per person.  The top line is total food supply.  The bottom line is an estimate of what people might actually be eating.  As the title of slide indicates there has been about a 19% increase sine the early 1980s.  This is equal to about 400 calories per day!

Clearly these are average statistics and there is all sorts of individual variability related to what people eat.  However, the story for society as a whole is pretty alarming.  If these changes in consumption are not offset by at least some increased energy expenditure this would work out to a pound of weight gain every 9 days or about 40 pounds (18kg) per year based on the idea that a pound of fat is 3500 calories of excess energy consumption.



The USDA statistics about increased calorie consumption have been challenged and better estimates are shown below for all adults (ALL), normal weight (NW), overweight (OW), and obese (OB) adults in the U.S.  These data compare estimates made in the early 1970s to data from 2005-2006.




So, if we use these data, about 200 calories per day, then we would expect people to gain about 20 lbs (9kg) per year.  Also remember from my earlier posts only about 5% of people are meeting the guidelines for physical activity and there has been an average loss of about 100-150 calories a day of physical activity at work for many people.

When you see statistics like this the question isn’t why is the population getting fatter, the question is why isn’t the population getting even fatter!


We are less fat than predicted!

The figure below shows the average adult is “only” about 10kg heavier now then in the early 70s when caloric consumption starts to rise.  This figure comes from an excellent paper with a lot mathematical modeling on how and why our energy expenditure goes up when we eat too much and why it goes down when we diet.


1975                                                                                                          2010


Here is a link to a simulator you can use to project changes in your body weight with dieting using the computer models that generated the simulated changes in body weight noted above.

So the good news is that it is actually pretty hard to gain weight and that  the combination of a lot of extra calories and a lot less activity is required to pack the pounds on.  The bad news is that these same principles apply in reverse and make it hard to lose weight.   The figure below from the modeling paper is an example or what happens to most people when they try to lose weight.

The bottom panel shows a baseline energy consumption of 10 Mega Joules or about 2500 calories per day.  Dieting starts and people reduce their caloric consumption by 30-35% but unless they really start to exercise the energy consumption also goes down.  After a couple of months their eating begins to pick back up, but energy expenditure is still down and weight begins to creep back up over the next couple of year.   This pattern of weight gain is shown in the top panel.  The other interesting thing is just how much inter individual variation there is both total weight loss, energy expenditure and how they interact over time.



The concepts outlined in this figure explains why the National Weight Control Registry data on successful long term “losers” shows that a combination of a low calorie diet and high levels of physical activity are required to take and keep weight off over time.  In coming posts I will try to figure out where the extra calories are coming from over the last 30-40 years and why there is not a linear relationship between eating less (or becoming more active) and losing weight.


4 Responses to “What About Diet?”

  1. September 3rd, 2012 at 10:06 pm

    Blogrolling – Dr. Michael Joyner-Style | On Becoming a Domestic and Laboratory Goddess says:

    […] packed with information that even the well-read layperson will find useful.  Go check him out (here) and tell him Isis says hello. Rate this:Tell your friends:EmailDiggLike this:LikeBe the first to […]

  2. September 4th, 2012 at 6:58 am

    Sheila Ray says:

    Mike, I have a theory that is only anecdotal. I have not found a study to confirm it, but I have seen it several times in my business. We’ve all heard a calorie is a calorie is a calorie. I’m no longer convinced this is true. I believe the quality of the calorie comes into play, especially with weight loss and healthy weight maintenance. I’ve seen people who workout at a moderate to vigorous level 5 days/week for 60 minutes/session and who eat the right amount of calories that, combined with their activity level, should be losing 1-2 pounds per week and they do not. Then, I’ve seen these same people not change their exercise or their quantity of calorie intake, but change the quality of calorie intake and the pounds start to melt off. Avoiding processed foods, chemicals, and artificial ingredients seem to have a favorable effect. It is quite interesting.

  3. September 4th, 2012 at 7:36 am

    Michael Joyner, M.D. says:

    Sheila, the topic of whether all calories are created equal is a big issue both scientifically and for the practical reasons you mention. I will devote more space to this in the coming weeks but four factors come to mind:

    1) When your body stores carbohydrates as glycogen it also stores a significant amount of water. This is one of the reasons people get a big initial weight loss on low carb diets. Glycogen stores go down and the water goes with it.
    2) You actually burn calories digesting food and the amount you burn may vary by food type or composition.
    3) Differing effects on appetite and how “full” you feel.
    4) Anything that reduces food choices and variability makes it harder to eat too much. So getting rid of carbs or fats reduces choices and may make it easier to stick to a diet.

    From a big picture perspective successful “losers” are on low calorie diets and that the four factors I mention above can help people stick to their diets.

  4. September 5th, 2012 at 3:03 pm

    Joey Keillor says:

    Totally anecdotal, but I remember going to McDonalds as a kid and if you got a small pop (soda for those not from MN), you got a small glass half full of ice and if you wanted another pop, you paid for it. Then the idea of free-refills came along (to my delight) and you could slug down 1,000 calories without a second thought.

    In general, I think that our notion of what constitutes a “meal” has gotten much larger and we mostly don’t even realize it.

Leave a Reply