Do Carbs and Insulin Really Make You Fat?

After the low-fat craziness of the 80’s and early 90’s, the pendulum swung in the opposite direction. All of a sudden, carbs were public enemy number 1! The theory was simple: refined carbohydrates raise insulin levels. Insulin causes fat storage. Therefore, keep insulin levels low by eating a low-carb diet and avoiding high-glycemic foods and you will lose weight. While it seems simple enough, but is it true? Let us see what the latest research has to say…

In August of this year, The American Journal of Physiology-Endocrinology and Metabolism published an article: "Calories in, calories out" and macronutrient intake: The Hope, Hype, and Science of Calories.

Here is what the researchers Scott Howell and Richard Kones concluded:

Strong data indicate that energy balance is not materially changed during isocaloric substitution of dietary fats for carbohydrates. Results from a number of sources refute both the theory and effectiveness of the carbohydrate-insulin hypothesis. Instead, risk for obesity is primarily determined by total calorie intake.

In plain English, this means that your body weight is really about how many calories you eat. If you eat the same amount of calories (and I would add protein) then how many carbs vs. fats you eat is not as important.

If you have read much on nutrition or fat loss over the years, then after reading that, you have the following questions:

Why does every diet book seem to target something other than calories?

The book publishing business is about creating something new, exciting and novel. A book entitled, “Eat Fewer Calories to Lose Weight” is not going to make the New York Time’s best-seller list. In addition, many people have learned that one of the easiest ways to make a quick buck in the fitness or weight loss industry is to tell people what they want to hear. Everyone wants to believe there is a fast, easy secret to weight loss just waiting to be discovered.

Many people fail to see the common denominator between all diets. Whether you eat low carb, low fat, “clean”, wheat-free, gluten-free, sugar-free, paleo, keto, vegan, IIFYM (if it fits your macros), do a cleanse or fast intermittently, you end up (at least initially) eating fewer calories. That is what causes the weight loss.

Related: The Diet Deception

Does this mean we should throw out the glycemic index?

Not necessarily, but we over-emphasized its importance. One of the main problems with the glycemic index is that the research was done with just eating carbs. However, we don’t (or at least we shouldn’t) eat just carbs at a meal. When you throw in protein and fats, the insulin response changes. The glycemic index has helped some people choose more whole-natural sources of carbs and limit highly-processed foods. This is a good thing for your health, body composition, and performance. Although I do not do medical nutritional therapy, the glycemic index and glycemic load can still be helpful for diabetics.

Another potential mistake we made with the glycemic index is to ignore the importance of satiety. Some foods leave you feeling much more satisfied and less likely to binge later. One of the most satisfying carbs is potatoes. In the glycemic index-craze days, we demonized potatoes for having a high glycemic index. However, in satiety research, they were amazing at filling you up - thus preventing future over-eating.

For more information on the satiety index, check out: A Simple, Overlooked Key to Easier Fat Loss Nutrition

If you are not familiar with the glycemic index and glycemic load, I wrote about it years ago HERE.

Does this mean I can eat whatever carbs I want and not gain weight?

No. Many high-sugar foods and highly-refined carbohydrates taste amazing. For some people, they can be downright addicting. In addition, they are calorically dense and very low in fiber. As a result, these foods do a very poor job of “filling you up” and are very, very easy to overeat – which puts you in a calorie surplus. It is this surplus, more than the insulin that is causing the weight gain.

It is also important to remember that that nutrition is about more than just the number you see on the scale. Your food choices will affect your health, performance and overall quality of life. Refined carbohydrates are deficient in fiber, vitamins, minerals, antioxidants, and phytochemicals. Today's highly-refined junk foods are down-right unhealthy and should be limited to occasional treats in small amounts. 

You also need to pay attention to your individual response to different foods. The more I learn about nutrition and the longer I work with people, the more I realize how different we are when it comes to how we respond to certain foods. If certain carbs create stomach discomfort or make you feel gassy, bloated or sleepy (the sign of a sugar crash), they are not good for you.

Why do so many studies show that low carb is better than high carb?

Many of the earlier low-carb vs high carb studies failed to use equal protein levels. Protein is very thermogenic. This means you burn significantly more calories digesting protein and thus if you eat the same amount of calories, but eat less fat or carb and more protein, your net calorie balance changes.

The other reason for this trend in the literature is that most studies were short-term. Low-carb beats low fat – in the short-term (I’ll explain more why below…). However, things change with longer-term studies. Back in 2014, the Annals of Internal Medicine did a 12-month study comparing low-carb and low-fat groups. The low-carb group saw faster results (pretty much all the changes were in the first 3 months), but they were only slightly better by the end of the 12 months. Note: the lower-carb group also had some health benefits related to the risk of heart disease (this again comes back to my previous point that nutrition is about more than just your scale weight).

Why do I lose weight when I cut carbs and gain weight when I add carbs back in my diet?

Always remember weight loss does not necessarily mean fat loss. Drastic weight gain or weight loss is not a change of body fat levels. This takes more time.

Your body stores carbs as glycogen in your muscles and liver. When you cut your carb intake, your body will quickly use up most of your stored glycogen. For every molecule of glycogen, your body also stores 3-4 molecules of water. As a result after a week of low-carb dieting, you can be down several pounds, but those pounds are glycogen and water – not fat. If you have been eating low carb and return to a higher carb intake, you will notice rapid weight gain. Again, this is not a rapid gain in body fat, but rather rapid regain of glycogen and water.

Related: The Worst Weight Loss Mistake

Practical Applications for You and Your Body Composition

Note: I have written about many of these practical applications in other posts. This section is full of links to those posts to give you more details and to keep the length of this post down.

1. If you are trying to lose fat, don’t get distracted with all the fads and silliness of the weight loss industry.

The Diet Deception

2. Forget about jumping on and off diets. Instead, focus on the gradual adoption of effective life-long habits for fat loss.

Secret to Permanent Weight Loss

30 Habits to Get and Stay at Your Ideal Weight for Life

7 Habits of Highly Lean People

52 Weeks to Better Nutrition and a New You!

3. Focus on first on creating a calorie deficit.

6 Simple Ways to Reduce Your Calories Without Counting Them

4. Shoot for about 0.75-1g of protein per pound of ideal body weight

Eat More Protein, Lose More Fat

5. Play with different ratios of fats and carbs to find what works best for you.

Some people do better with a higher fat, lower carb diet while others do best with a lower fat, higher carb diet. Here is a list of other things you should consider when determining your optimal ratios of proteins and carbs:

• Health
• Body composition 
• Amount of physical activity
• Energy levels
• Satiety
• Training performance
• Work/life performance
• Mental clarity/efficiency
• How you feel after you eat
• Gut health
• Blood sugar levels (you can go by how you feel or get a blood glucose monitor)

The key is knowing which carbs are good and not good for you. Besides the obvious junk foods, I know a number of generally considered "good carbs" that I avoid - simply because I know I don't feel well when I eat them. You need to come up with this list for you.

The 1-2 Hour Test

The New Rules of Carbs

Healthy Fats

6. Monitor body composition, not just scale weight

If you can get an accurate body composition assessment – great! If not, at least add a waist measurement (ladies: do waist and hips) to your scale weight to get a better idea of what is going on.

Assessing Body Composition

7. Follow an effective exercise plan for fat loss

Reference and Additional Resource: 

Do you want to dive into fat loss research further? Check out Brad Schoenfeld’s presentation: Facts and Fallacies of Fat Loss from the NSCA’s 2016 Personal Trainers Conference.