You may have come across the number-heavy article from CNN recently, Where Fat Goes When You Lose Weight.
It describes that fat is chemically broken down into carbon dioxide and water, and oxygen is used in the process, meaning we exhale most of the fat we’re burning. True, and something all dietitians and doctors learn in biochemistry courses. Granted, we don’t sit there explaining the molecular breakdown of fat to very many patients or clients regularly, because really why would we?
The article then goes on to explain how the food and water and oxygen we take in, needs to be equal to or less than the water and carbon dioxide we exhale (or sweat and urinate away), or we gain weight. Still true. But then it gets more complicated than this author lets on.
What isn’t mentioned are all the factors that influence how much food you’re biologically driven to consume and the many factors that influence changes in your body’s metabolic speed. Without these important considerations, it’s easy to think that weight loss is easy, simple and your own fault if you aren’t able to do it. Nothing could be further from the truth. So I want to take some time to shed more light on some of these factors, which show you why simple math formulas can quickly turn complicated when it comes to the human body.
Calories In, Calories Out
According to simple math, you should be able to lose weight no matter what you eat as long as it’s less than what you put out, even if it’s a diet of – twinkies?? Well, yes. In 2010, Mark Haub, a professor of human nutrition at Kansas State University did just that. You can read about The Twinkie Diet here, but the point is that he was able to lose 27 pounds and improve his cholesterol profile eating snack cakes and sugary cereals over 2 months.
Now before you go out and load up on Twinkies, there are some things to realize. We don’t know other potential health impacts of this type of diet over the long term, particularly the impact on the gut microbiome (more on that later). We do know from years of data and spreading the message to “just eat less,” that it hasn’t worked. The rate of obesity is again on the incline, and we all know the diet industry is booming. One big reason for this, is the body’s natural desire to eat – especially when it perceived that food and nutrients are scarce.
1. Appetite Hormones
When food is consistently restricted over time, the body increases the hunger hormone called ghrelin, and decreases the satiety hormone called leptin. This makes you extra hungry, and you may find yourself thinking of food often. While the type of food you eat may not directly change the metabolic equation, it certainly impacts your appetite, and therefore how likely you are to stick with consuming less than you need. Some research has shown that a diet higher in fiber and protein and limited in fat can suppress appetite, even when calories are moderately restricted. However, omega-3 fatty acids have also been linked to lower appetite levels.
There’s also evidence that eating “hyper-palatable food,” usually highly processed food containing combinations of fat, sugar and and/or salt, designed to get us hooked, aka “junk food,” may promote binge eating. And it’s been shown that a diet low in carbohydrates increases carbohydrate cravings. Clearly, the type of food consumed can have an important impact on appetite, which in turn can predict how successful someone will be on sustaining a weight loss diet.
2. Metabolic Slowing
It’s well accepted in the medical and nutrition sphere that weight loss slows metabolism. In fact, you need less oxygen when you have less fat mass, so you consume less of it than you would when you had some extra fat. Interestingly, this lower metabolism and lessened oxygen uptake may reduce oxidative damage in the body, and explain why limiting calories may slow the aging process. The point is that how much food (and oxygen) you need will change with changes in body fat and weight. So while the formula holds true, that you still must expel more than you take in, how much that actually is will change based on how much you weigh. It also changes based on your activity level, as described in the article.
3. Previous Weight Loss
The other interesting (and frustrating) factor to keep in mind is that even if you take two people of the same weight and gender and activity level, the only major difference is that one has been that weight all her life, the other lost 60 pounds to get to that weight. Are their metabolisms the same? Will they be able to eat the same amount of food and do the same amount of activity to maintain that weight? If you have ever been that person trying to maintain a big weight loss, you probably already know that the answer is most likely NO.
We have some important information on this from the Biggest Loser participants, most of whom have gained weight back within several years of losing it. A small study showed that not only was metabolism much lower after the weight loss, it continued to decrease over the following 6 years. One participant burned 800 fewer calories than what is expected for a man of his size. Granted, this is just one small study and didn’t have a control group (an important thing in research), but it could shed light on why it’s so difficult for those who have lost a large amount of weight to keep it off. Add to that the increases in hunger hormone and decreases in satiety hormone that persist after a large weight loss, and you can see the struggle is real.
4. Nutrition and Metabolism
Can nutrition affect your metabolism? Most certainly, since a number of nutrients are necessary for energy metabolism to take place. Most of the B vitamins, choline, iodine, chromium, manganese, iron, zinc, copper, and vitamin K are all part of the process. Missing out on these regularly could interfere with normal metabolism, even if enough calories are present.
5. The Microbiome
The food we eat has a direct impact on the types of bacteria living in our gut, called the microbiome. The microbiome of obese individuals is different from those of lean individuals, and the bacteria of those who are obese uptake more calories than the bacteria of those who are lean, leading to higher absorption of calories from the diet. Eating food high in dietary fiber and low in added sugars and fats can help the healthy bacteria flourish, while a diet high in trans and saturated fat and excess sugar promotes the obesity-related bacteria. It would be interesting to see the microbiome before and after the twinkie diet!
To make things even more complicated, exposure to certain hormones will affect how your body burns or holds on to fat. Prolonged exposure to the major stress hormone, cortisol, has been linked to higher fat mass, and it’s also indicated in belly fat. Cushing’s syndrome, which is characterized by elevated cortisol levels often leads to weight gain, especially in the belly and neck area. Research has shown that interventions in mindfulness to lower stress can also reduce abdominal fat.
7. Eating Speed
How fast you eat may play a role in weight gain, and research has correlated faster eating with more weight gain and metabolic diseases like diabetes. This doesn’t mean that fast eating necessarily caused the weight gain, but it makes sense that more calories would be consumed if you eat quickly. It takes the body around 20 minutes to recognize the feelings of satiety. Eating fast makes it likely to intake a lot more calories before reaching the 20 minute mark, when you get that message to stop.
8. Eating Late at Night
Several studies have correlated high body fat with eating late at night, and several animal models have shown that night eating can disrupt metabolism through disruption of the circadian rhythm. There’s a lot of conflicting research in meal timing, especially during regular waking hours. The stronger connection appears to be when eating during regular sleeping hours, as the body may not process food as well at this time.
Getting enough sleep has also been connected with weight management, and lack of sleep is associated with weight gain and higher risk of diabetes. Part of this can be explained by changes in the hunger and fullness hormones with sleep deprivation. There’s likely an interplay between lack of sleep driving higher calorie intake and actual metabolic changes that promote weight gain.
Now, this absolutely doesn’t mean you should give up hope. Even though weight loss is complicated, it’s not impossible. Research (and experience) shows that making lifestyle changes is greatly increased with the help of a health coach, (27) and a big part of that is the relationship and trust you build with someone who has your best interest as their focus. But I also think that many of us place too much importance and hope on the scale alone. You can improve your health and energy by focusing on healthy behaviors, whether or not you lose weight.
To sum it up, there are many factors to consider when you want to lose weight, and what you eat plays a big part for most people. Eating a diet that promotes satiety, provides the nutrients needed for healthy metabolic and hormone function, and that feeds the healthy bacteria along with eating more slowly, avoiding eating late at night (during regular sleep hours), getting enough sleep and reducing stress, are all important considerations for long term success. The complexity of the human body makes simple weight loss equations impractical at best, and insulting at worst.