by Nancy Clark, MS, RD, CSSD
“I can’t lose weight like I used to. I must be eating too many carbs”
“Do you think a keto diet is a good way to drop a few pounds?”
Judging by the phone calls I get from potential clients, an increasing number of runners of all ages are complaining, “Why can’t I do something as simple as shed a few pounds???” They are frustrated and at a loss about what to do to lose undesired body fat.
Speaking at the annual meeting of the American College of Sports Medicine (June 2021; www.acsm.org), Kevin Hall PhD explained that fat loss is far from simple. Dr. Hall works at the National Institutes of Health. His laboratory investigates how metabolism and the brain respond to a variety of changes in diet and exercise. His research has helped identify the complex mechanisms that regulate weight.
Weight loss is not simple
You’ve likely heard, “A pound of fat equates to 3,500 stored calories. To lose one pound of body fat a week, you can simply knock off 500 calories a day—or burn off 500 calories more than usual, or some combination of the two.” Hall explained the “simple” approach to weight loss just doesn’t hold true. Runners who are chronic dieters would have shriveled up and disappeared by now. Not the case.
Weight loss is not simple because our bodies adapt to “famines” by conserving energy. When food is scarce, be it a famine or a diet, the body conserves energy (metabolism slows, spontaneous movement lessens) and simultaneously appetite increases. Hence, eating less (dieting) takes persistent effort. The greater the energy deficit and the greater the weight loss, the greater the increase in appetite. Losing weight becomes more and more challenging. Hence, most runners end up unwilling or unable to sustain for a long time a diet with a calorie reduction of 25%. For a typical female runner who maintains weight at about 2,400 calories, that’s an 1,800-calorie reducing diet. Based on my experience, runners inevitably self-imposed a 1,200 – 1,500 calorie reducing plan. No wonder their diets fail! The stricter the diet, the hungrier the dieter, the bigger the backlash. The runner ends up devouring way too much ice cream, too many cookies, chips…
The bottom line: Runners who diet commonly end up heavier. You want to learn how to eat competently by working with a registered dietitian (RD) who specializes in sports nutrition (CSSD).
Is keto the answer?
So often I hear frustrated runners ask, “What if I just do keto (or Paleo or another trendy diet) for a bit and then go back to eating “normally?” Ha! When runners have managed to successfully lose weight, they can’t go back to eating like they used to eat. These dieters need fewer calories to support their lighter body. For each kilogram (2.2 lb) of weight lost, a dieter requires about 25 fewer calories/kg per day. Hence, runners who lose 10 kg. (22 lbs.) need about 250 fewer calories per day to maintain their new reduced weight. Unfortunately, appetite-regulating hormones nudge them to want to eat more than that. This gets to be a tiring fight, and most folks lose the battle of the bulge.
The bottom line: Preventing weight gain in the first place might be simpler than trying to reclaim a former physique!
Are carbs the problem?
What if you could lose weight by cutting carbohydrates but not calories? Diet gurus have promised this for years, as do today’s keto supporters. Anti-carbers claim high-carb diets lead to excess insulin secretion, hunger, excessive eating, and fat gain. Low-carb/keto diets are touted to reduce insulin, hunger—and promote easy fat loss.
Not so simple. Despite popular belief, simply knocking off starches (bread, pasta, grains) and sugary foods does not guarantee fat loss—unless it creates an energy deficit. That is, eliminating a serving of rice from dinner can knock off 200 calories. But does the hungry dieter then indulge in a pint of sugar-free ice cream or a keto-bomb? The carb-free = calorie-free attitude can easily wipe out the deficit created by cutting out carbs.
Hall’s research (1) does not support the carb-insulin theory that carbs are fattening. He closely monitored subjects in a metabolic ward who ate as much as they desired of high (75%) carb/high-glycemic diet designed to spike blood glucose and trigger high levels of insulin. The subjects did not gain body fat. In fact, every single subject eating the high carb/high insulin/low fat diet ate, on average, about 700 fewer calories/day less than when they ate the high fat/low carb/low insulin keto diet.
The bottom line: Carbs are NOT inherently fattening. (If carbs were fattening, then people in Asian countries who eat bowlfuls of rice would be obese. Not the case.)
If carbs aren’t fattening, what is?
The increase in obesity in the US correlates well with the increased intake of ultra-processed foods. Hall is pointing his finger at foods such as Oreos, soda, instant ramen noodles, chicken nuggets, etc. He has researched the impact of two weeks of an ultra-processed convenience food diet vs. two weeks of a homemade, natural foods diet. (2) The menus were very carefully designed to be equally tasty. The subjects reported no differences in pleasantness between the two diets. They ate as much as desired.
With the ultra-processed diet, the subjects consumed about 500 more calories a day compared to the unprocessed diet. They gained weight during those two weeks—and lost weight (without trying to do so) with the unprocessed diet. Because both diets offered the same amount of sugar, carbs, and fat, those nutrients did not drive the weight change.
What’s going on? Hall is currently looking at why ultra-processed foods easily lead to weight gain.
The bottom line: Until we know more, your best bet is to limit ultra-processed foods. Fret less about sugar/carbs, and more about the processing. Somehow, find time to prepare meals. As a parent, please teach your kids to cook. Hopefully you’ll all enjoy the eat-well, stay lean diet!
Sports Nutritionist Nancy Clark, MS, RD counsels both casual and competitive athletes in the Boston-area (617-795-1875). Her best-selling Nancy Clark’s Sports Nutrition Guidebook can help you learn to eat wisely and well. Not a book-reader? Enjoy her online workshop at NancyClarkRD.com
1. Hall, K. et all. Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake. Nat Med 2021 Feb;27(2):344-353
2. Hall, K. et al. Ultra-processed diets cause excess calorie intake and weight gain: An inpatient randomized controlled trial of ad libitum food intake. Cell Metab 2019. 30(1):67-77.