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5 Reasons Low-Calorie Diets Don’t Work Long-Term

Weight management is more than calories in, calories out.

Unless you’re a pro-level athlete who needs to ensure you’re eating enough calories, there’s probably no good reason to count calories or follow a calorie-based meal plan.

I know…you know someone who lost weight counting calories. Maybe you did yourself. Do you know anyone who kept the weight off for a year or two by continuing to count calories?

I doubt it.

The premise behind calorie counting is that you can measure the calorie content of the food you eat and compare it to the calories you burn. If you burn more than you eat, you’ll lose weight.

It sounds simple, which is why this concept doesn’t die. However, this isn’t the way your body or the food you eat works. 

Most importantly, the calorie count of the food you eat has a marginal, if any, impact on your body fat. Instead, the macronutrient makeup is what matters.

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The Calorie Balance Equation (A Quick Refresher)

You eat calories. You burn calories.

According to the calorie balance equation, if you burn more calories than you eat, you lose weight. If you eat more calories than you burn, you gain weight.

Let’s assume you eat 2500 calories per day and want to lose 12 pounds of muffin-top-making body fat in 12 weeks.

One pound of fat contains 3500 calories. So, the theory is, if you create a 500 calorie per day deficit or a 3500 calorie per week deficit, you’ll lose a pound per week.

For a calorie-based meal plan to work,

  • You must be able to count calories in the foods you eat accurately
  • You must be able to measure the calories you burn during the day accurately
  • Your body must manage its fat stores only based on the deficit or surplus of calories you create

As you’ll see, none of this is reality.

1. Calorie counts are not accurate.

The accuracy of each ingredient’s calorie content in a recipe varies, making the calorie count of an entire meal, like the one you’d order at a restaurant, significantly inaccurate.

A study published in the Journal of the American Medical Association found that almost 20% of restaurant’s calorie-counts were understated by at least 100 calories.

In another study, published in the Journal of the Academy of Nutrition and Dietetics, restaurant meals contained an average of 18% more calories than what the menu stated, and frozen foods contained an average of 8% more than what the labels stated.

When you’re trying to create a 500 calorie deficit in a day, that’s a significant number.

“Ok, I get that there’s variability at restaurants, but the foods I buy and cook will still be accurate, right? After all, the FDA ensures all food labels are accurate before companies sell the foods, right?”

No and no.

The following are a few questions and answers straight from the FDA:

From Guidance for Industry: A Food Labeling Guide by the Food and Drug Administration (FDA)

Can I use “average” values derived from databases to determine the nutrient content of my product? 

FDA has not stated how a company should determine the nutrient content of their product for labeling purposes. Therefore, there is no prohibition from using “average” values for its product derived from databases if a manufacturer is confident that the values obtained meet FDA’s compliance criteria. Regardless of its source, a company is responsible for the accuracy and the compliance of the information presented on the label. Use of a database that has been accepted by FDA affords a firm some measure of security in that the agency has stated that it will work with industry to resolve any compliance problems that might arise for food labeled on the basis of a database that the agency has accepted. A manual entitled FDA Nutrition Labeling Manual: A Guide for Developing and Using Databases is available online. 

How many samples of each product should we analyze for nutrition labeling?

FDA has not defined the number of samples that must be analyzed. It is the responsibility of the manufacturer/packer/distributor to determine the variability of their product(s) and the number of samples needed to provide accurate nutrient data. The FDA Nutrition Labeling Manual: A Guide for Developing and Using Databases, available from FDA, may be of assistance in this area. FDA will use a composite of 12 units when performing enforcement analyses. 21 CFR 101.9(g) 

May I copy my competitor’s label? 

Firms are responsible for the accuracy of the Nutrition Facts label and there is no assurance that the data from a competitor’s product is valid for another product. Products of a similar nature are not necessarily equivalent in ingredients and nutrient value. If FDA found a product to be out of compliance because a firm merely copied its competitor’s label, the firm would be hard pressed to prove that they labeled the product “in good faith.” 

Will FDA analyze my products and send me a report to use for my nutrition label?

No. FDA does not have the resources to analyze products upon request. However, FDA will collect surveillance samples to monitor the accuracy of nutrition information. The manufacturer, packer or distributor would be advised of any analytical results that are not in compliance. Additionally, depending on circumstances, FDA may initiate regulatory action. 

Does FDA provide database information to industry? 

No. FDA will review and accept industry databases which remain the property of the organization that developed and submitted the data. (In other words, the “industry” can create the facts, then the FDA uses those facts to audit the industry.)

The nutrition facts are there to make you feel good, but the FDA doesn’t have the capacity, nor the interest in making sure the numbers are accurate.

Checking calorie counts might help you choose Halo Top over Ben & Jerry’s. That’s good.

But I’ve met too many people who fuss over the 10 calories in a dry rub seasoning because it’ll put them 10 calories over for the day on their calorie goal. They’re probably off by 10-20% already, so the fuss over the seasoning creates an unnecessary stress.

2. Low-calorie diets overlook the importance of macronutrients.

When I work with people on their nutrition, I almost always have them start with eating more protein. That often surprises people, especially those looking to lose weight. They often ask, “Won’t eating more protein make me fatter if I end up eating more calories than I already am?”

The truth is, it’s almost impossible to get fat from eating more protein. It’s easy to get fatter by eating too much fat and/or carbs.

The impact of overeating protein

Dr. Jose Antonio and his research team took a group of young adults split them into two groups:

  • a control group who maintained their current exercise, lifestyle, and diet (in which they ate about 1.0 gram of protein per pound bodyweight)
  • a high-protein group, who maintained their exercise, lifestyle, and diet, but then added enough protein so that they consumed 2.2 grams of protein per pound body weight (this is a massive amount of protein)

By increasing their protein intake, the high-protein group added about 800 calories per day to their diet. According to the calorie balance equation, an 800 calorie surplus should have made them gain 1.6 pounds of body fat per week, or almost 13 pounds, during the 8-week study.

How much weight did they gain? Zero. None. Zilch. Nada.

Their body composition remained the same.

Even if they’d gained a little weight, the results would have still flown in the face of the calorie balance equation.

The impact of eating low-calorie, low-protein, high-carb

I liken this to the traditional Weight Watchers way of eating. In the past, they listed higher protein foods as some of the highest-point options. As a result, people avoided protein-rich foods and ate low-fat, high-carb foods instead.

Did they lose weight? Yes. Did they feel good? No.

Did they look good? With their clothes on, they looked thinner. In workout gear or swimsuits, many people looked skinny-fat. Their body fat levels remained quite high as much of their weight loss involved muscle loss.

The worst part was, they eventually regained the weight, and then some, even if they tried eating low-calorie long-term.

To be fair to Weight Watchers, their points system is better today. Their “Zero Point” list includes many lean protein sources, which should help people eat a higher-protein diet than in the past. That said, I’m definitely not recommending Weight Watchers.

A healthy and fit person can get away with eating a low-protein, high-carb diet for a while. Eventually, though, the impact of such a diet shows up in their elevated triglycerides, HbA1c, body fat, lack of muscle, fluctuating energy levels, and more.

For those who have metabolic syndrome, diabetes, or who are overweight or obese, a low-calorie, low-protein diet not only exacerbates their metabolic dysfunction, but it also leads to never-ending hunger and cravings.

A high-protein diet is better for weight loss than a low-carb or low-fat diet, which is why I focus on eating more protein over restricting carbs or fat for clients. It’s a lot easier to live with knowing you need to eat more of some foods than knowing you can’t eat much of others.

The types of calories, not the number, and their impact on your hormones, affect your body composition.

3. Low-calorie diets cause muscle loss.

Muscle mass plays a significant role in your metabolic rate. Muscle doesn’t burn the same quantity of calories as your brain, liver, or other organs, but you can’t do anything about the size of them. You can influence the size and amount of your muscle mass.

Muscle also stores carbohydrates as glycogen. The less muscle you have, the less capacity you have to store carbs. When you run out of room to store carbs, they raise blood sugar and triglycerides, increase fat storage, and contribute to fatty liver.

That’s why I always stress this point with my clients and online personal training members:

Don’t lose muscle!

Unfortunately, when people eat fewer calories, they tend to eat less protein, too. Unless they’re following a carnivore diet or another high-protein meal plan, they’ll likely lose significant muscle during their diets.

Less muscle leads to a lower metabolic rate, which means they’ll need to lower calories even more, or exercise more, to keep losing weight.

Eventually, they can’t handle the diet anymore, and even if they eat a moderate amount of food, they gain weight with lighting-speed.

4. Low-calorie diets can lead to thyroid dysfunction.

Your thyroid gland regulates your metabolic rate. Low-calorie diets suppress thyroid function, causing you to reduce T3 and T4 production as a protective mechanism.

This lowering of thyroid hormone is often called your body’s “starvation response.”

If you’ve been eating 2500 calories per day, and successfully lower your calorie intake to 2000 calories per day, in a matter of weeks, your thyroid production adjusts so your calorie expenditure matches your calorie intake.

This all too common scenario was the source of drama during The Biggest Loser. People would eat like a bird and exercise like an athlete. Then, they’d step on the scale and be shocked at the minimal amount of weight loss.

That’s your thyroid gland in action. What do most people do when the weight loss stops? They exercise even more and eat even less.

They experience a bit more weight loss, and then their thyroid production slows even more.

When you’re calorie-deprived, your thyroid reduces the secretion of T3 and T4 to conserve energy.

The impact on your thyroid function can be severe and long-term.

A recent study by Erin et al. showed that after “The Biggest Loser” competition (30 weeks), participants had a nearly 23% reduction of RMR, and after a 6-year follow up, RMR remained suppressed at similar levels as at the end of the competition, suggesting that potential metabolic adaptation might result in weight regain.

Gang Liu, et al. Thyroid Hormones and Changes in Body Weight and Metabolic Parameters in Response to Weight-Loss Diets: The POUNDS LOST Trial

Please read that again and let it sink in.

Six years after participating in the Biggest Loser, participants’ metabolic rates were still suppressed.

Why do people who repeatedly attempt low-calorie diets get progressively heavier each time they get off a diet? Because they progressively suppress their thyroid function.

That said, I’m only covering one hormone here. A low-calorie diet can also lower testosterone and growth hormone, raise cortisol, and mess up the hormones that control hunger and satiety.

5. Low-calorie diets cause mental dysfunction.

If the threat of muscle loss and hormone problems doesn’t have you convinced that low-calorie diets are dumb, maybe the threat of mental dysfunction will.

The best evidence comes from Ancel Keys’ Minnesota starvation experiment in 1944.

Thirty-six men followed a three-stage diet study. First, they ate a diet of about 3200 calories per day as a maintenance plan. Then, Keys cut their calorie intake in half and severely limited their protein intake.

Note: Many diets today recommend calorie intakes of less than 1600 calories and consider them to be healthy, so 1600 calories, by today’s standards of nutrition, hardly seems like a “low-calorie” diet.

Their twice-daily meals included cabbage, potatoes, turnips, beans, pasta, and brown bread. They followed this diet for three months. Then, Keys added treadmill walking to their program for the next six months. After that, they followed a three-month refeeding plan.

In addition to turning their average physiques into skeletal versions of themselves, they also suffered weakness, low heart rates, swollen joints, hair loss, dizziness, and felt cold all the time. That’s just the physical effects.

They also developed an obsession with food, thinking about it, dreaming about it, and when mealtime came, acting in childish, possessive, strange ways.

They’d play with their food, coddle it, and lick their plates to get every last bit of nutrition they could from their meals.

They lost their libido and suffered severe depression as well.

Months after the experiment, many of the men dealt with disordered eating. Some ate all the time. Others binged until they got sick.

This isn’t unlike the effects others experience on a low-calorie diet, whether they’re trying to lose 200 pounds or they’re preparing for a bodybuilding competition. You should carefully consider the potential short-term effects on mental function and long-term obsession with food before going down the path of an unnecessary weight loss method.

Is there a better alternative?

So, if a low-calorie diet isn’t the best solution for long-term weight management, what is?

For a diet to be effective long-term, it needs to deliver results, but it has to be sustainable, and it has to be set up in a way where people don’t feel restricted.

That’s why I’ve had so much success with the practice of eating more protein. A higher-protein diet crowds out the other foods that make you fat. It also helps you maintain muscle as you lose weight, supports a strong immune system, and keeps you satiated.

That said, some people need something more strict than a high-protein diet, especially when they are dealing with metabolic syndrome or other metabolic dysfunction. In those cases, a strict carnivore diet may be more appropriate.

Once a client is consistent with a high-protein diet, I’ll often have them fine-tune things by going gluten-free, eating on an intermittent fasting schedule, or dropping dairy. And I always recommend the Foundational Five as well. Yet, that all comes after establishing the habit of eating more protein for most people.

Liu, Gang, et al. “Thyroid Hormones and Changes in Body Weight and Metabolic Parameters in Response to Weight-Loss Diets: The POUNDS LOST Trial.” International Journal of Obesity (2005), vol. 41, no. 6, June 2017, pp. 878–86. PubMed Central, doi:10.1038/ijo.2017.28.

Müller, Manfred J., et al. “Changes in Energy Expenditure with Weight Gain and Weight Loss in Humans.” Current Obesity Reports, vol. 5, no. 4, Dec. 2016, pp. 413–23. PubMed, doi:10.1007/s13679-016-0237-4.

Sarró – Those Courageous Boys 73 Years after the Minnesot.Pdf. Accessed 16 Feb. 2021. Sarró, S. Those Courageous Boys: 73 Years after the Minnesota Starvation Experiment. A Psychiatrist’s View. p. 10.

Urban, Lorien E., et al. “The Accuracy of Stated Energy Contents of Reduced-Energy, Commercially Prepared Foods.” Journal of the American Dietetic Association, vol. 110, no. 1, Elsevier, Jan. 2010, pp. 116–23., doi:10.1016/j.jada.2009.10.003.