There are many oft quoted pseudo-scientific ideas related to dietary advice in all media formats. Timing of meals for weight loss is promoted as an effective and critical factor in weight loss. The majority of the actual research is either contradictory or unclear. If you look at single lines of evidence there are studies that have persuasive conclusions. The total body of evidence is contradictory. Despite that, there are often media reports touting this marginally helpful advice. Time Magazine online recently published an article by author Alexandra Sifferlin titled”For Weight Loss Success, Think About When, Not Just What, You Eat.“.
Like most science reporters nowadays she is not a scientist, or a science expert. She commonly writes on science. She does fairly well, often her articles are quite good. Dietary research is something of a blind spot for her. This one, unfortunately, falls into the category of exaggeration. Since the research findings have been spread across the internet as dietary gospel. I think it is about time to ground the level of enthusiasm related to this study.
Her article presents the findings of a recent study. “In a study published in the international journal of obesity the scientists monitored 420 overweight participants on a 20-week weight loss program in Spain. The volunteers were split into two groups: early-eaters and late-eaters. Since lunch is considered the largest meal in Spain–about 40% of the day’s calories are consumed in the mid-day meal–half the participants ate lunch before 3 p.m. while the remainder ate lunch after 3 p.m. The late-eaters lost less weight overall, and shed pounds at a slower rate than those eating earlier. Those eating lunch later were more likely to skip breakfast or eat fewer calories, while the timing of breakfast and dinner didn’t influence weight loss effectiveness for either group. The researchers also considered other factors such as total caloric intake, energy expenditure, the appetite hormones leptin and ghrelin, and amount of sleep, but found they were similar in both groups.
One of the most common forms of weight control advice is metabolic manipulation. It is a compelling narrative. You have a weight problem because; you eat too late, too few meals, too many carbs, too much fat, insulin production, glycemic index, leptin levels, basal metabolism… et al. Although intuitively we think that our body’s metabolism and/or specific nutrients trump caloric intake, this is not really true. Research indicates that the calorie-in portion is far more critical.
Weight loss is a simple formula, calories-in versus calories-out. The biggest effect on weight is through total calorie balance. Positive= gain weight, Negative= lose weight. There is a moderate ability to affect caloric balance through metabolic means. There are specific diseases, both metabolic and congenital, that affect our body’s ability to absorb and utilize calories. Most people with weight issues do not suffer from these diseases. Most people suffer from a positive calorie imbalance. Baseline metabolism is part of your total caloric consumption. Dietary timing may plausibly affect basal metabolism.
Baseline metabolism is your body’s underlying energy consumption. It’s the amount of calories that you spend just to keep yourself alive. Cost of digestion, pumping blood, thinking, breathing, clearing wastes. All of this has a bottom line calorie consumption. It stands to reason that if you increase your basic metabolic calorie consumption it will help you lose weight.
This is a very plausible theory but people vastly underestimate the efficiency of our metabolism. For example 180 pound male running an 9 min. mile for an hour burns about 950 cal. Three slices of pepperoni pizza, average size, is about 870 cal. Many people can eat three slices of pepperoni pizza. A far smaller number of people would be able to run for an hour at a 9 minute/mile pace. Running a 9 minute mile is a vigorous aerobic activity. A person who went walking for a similar duration but did something low-impact at 4 miles an hour would only burn 389 cal. Resulting in a complete negation of the exercise. Bottom line, the human body is relatively energy efficient. It is not difficult to “out eat” your exercise. It is very hard to out exercise a high calorie diet. Exercise is magnitudes better than any other method for altering our metabolic caloric use.
The variable evaluated in this study is meal timing. There is a lot of dietary theory about meal timing. The underlying theory involves altering the body’s metabolism. People assume that eating at night is “bad”. Small frequent meals are commonly recommended as “good”. Despite these commonly held beliefs there are no consistent positive or negative effects found related to timing.
Much of diet science and pseudoscience also gives the impression that basal metabolic manipulation methods are the key to weight loss. Name the late night diet supplement commercial of your choice. They are all mostly hypothetical and unproven. There is no better method to alter basal metabolic rate than exercise. All other factors combined are negligible when compared to exercise. When you eat has a drastically smaller effect than exercise. Proposing that eating on a particular schedule provides significant impact on weight control is implausible and not supported by the body of research.
There is a recurrent glaring problem in meal timing research. Self reporting of calorie consumption. Few subjects ever properly report the number of calories they eat each day. This dietary phenomenon of under-reporting caloric intake can make the task of interpreting research results confusing, since studies on depend on self-reported food intake data. The number of snacking “episodes” is especially suspect in some studies, since study participants often forget to report eating these little meals. Researchers have come to expect that the average study participant will under-report daily food intake by about 20%, and that the margin can be as high as 50% for overweight and obese subjects (Bellisle 2004). This study has the same overall limitation.
Self reporting makes data suspect. It places the findings of this study into the “maybe” category. Although there is a growing body of mice evidence showing better weight loss results from small frequent feedings. It does not automatically transition to benefit in people.
There are many factors that cannot be easily controlled for in this study. Culture, dietary choices, genetic variance, exaggerating of activity, and self reporting are all limitations. The participants received counseling, and this is more likely a major factor. The difference in weight loss was 2% higher in early eaters Vs. late eaters. Although statistically significant the difference in total weight loss was small. Reporting variation could easily account for the difference. This study was 420 people over 20 weeks. 20 weeks is a very small number for weight tracking.
In my opinion I am not swayed by this study. More research is indicated. This type of research helps us better refine weight loss programs. It is not a panacea or a magic bullet for weight loss. Despite the title of the article, timing of meals is still marginally important compared to exercise and total calories.
In the United States obesity, and obesity related illness is a growing problem across all races, ages, and economic groups. I am continually concerned by the media drumbeat of fringe and inconsequential dietary findings. It produces a general culture of diet misinformation and frustration. Contradictory and confusing advice results in a population that is ripe for snake oil purveyors. There is nothing sexy or popular about the real obesity solution. We need to exercise more and eat smarter by focusing on a high fiber, low calorie diet. A diet that satiates and is maintainable. No one gets on the six o’clock news with that story, but it is the truth.
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