Why Not Everyone Responds the Same to Diet

Why Not Everyone Responds the Same to Diet

Low-fat, low-carb, Mediterranean, Paleo, DASH – welcome to the wonderful, confusing and misleading world of diets. Experts continually argue back and forth about what diet is best for weight loss and weight maintenance. Plus, diets fall in and out of favor based on the latest research. Why is there so much conflicting information on what diet plan is best for weight control? Probably because each of us has unique genes and a slightly different biochemical make-up. That’s what makes us individuals. As such, what works well for one person may be a dismal failure for another.

It’s a well-known fact that not everyone responds the same to a diet. Person A may lose 20 pounds on a particular diet plan while person B struggles to lose even 5 pounds. Some people have no success on a low-fat diet, but lose weight on a low-carb, while others slim down eating moderate quantities of carbs as long as they watch their calorie intake.

One reason studies sometimes find conflicting results as to what type of dietary approach works best likely has to do with genetics. Most studies don’t control for individual genetic variations. People also differ in the type of weight they lose. One person may lose body fat, while another loses a higher proportion of lean body mass, especially if they aren’t doing resistance training. There really is no “one size fits all” when it comes to diet.

 Metabolically Healthy and Metabolically Unhealthy: Why It Matters

Nothing could be more frustrating than reducing your calorie intake and not losing a single pound. A number of overweight and obese people experience this problem. One of the most common reasons overweight and obese people struggle to lose weight is they suffer from insulin resistance. Up to 60% of people who are above their ideal body weight are insulin resistant, at least to some degree.

Insulin is a hormone that opens up the “doorway,” actually a receptor, of a cell to let glucose in. Without insulin, glucose stays in the bloodstream and cells can’t get the energy they need. People with insulin resistance have too much insulin hanging around in their body. High levels of insulin cause cells to become less responsive to the effects of insulin and glucose can’t get into cells as easily. The “hungry” cells scream out for glucose, but the cellular doors won’t open up to let it in.

Insulin is also a fat storage hormone and with insulin levels being higher than normal and not dropping fast enough, fat burning grinds to a halt and dietary macronutrients are more likely to be stored as fat rather than burned for fuel. Body weight rises, insulin resistance increases in response to weight gain, and it turns into a vicious cycle that makes weight loss nearly impossible. With insulin resistance, the “calories in, calories burned” theory breaks down. Reducing calories isn’t enough for people with insulin resistance to lose weight because higher levels of insulin make it hard to break down fat.

People with insulin resistance usually respond best to a low-carbohydrate diet, or at least a low-glycemic, fiber-rich carb diet. A low-carb diet helps to minimize the release of insulin in response to a meal so that cells gradually regain their sensitivity to insulin and the weight begins to come off. Exercise, too, helps improve insulin sensitivity and correct the underlying metabolic issues. People who are metabolically healthy may lose weight on a low-fat diet, as long as they reduce their total calorie intake, but people with insulin resistance typically can’t. That’s because metabolically healthy people don’t have the added problem of insulin resistance to deal with. Low-fat diets are higher in carbohydrates, which can further fuel insulin resistance.

Even Stress Can Impact How Your Body Responds to What Your Diet

When you’re chronically stressed, don’t get enough sleep or push your body too hard through exercise without allowing it to recover, your body’s response to diet changes. Stressful situations such as these cause your adrenal glands to pump out more cortisol and your cortisol level rises. When cortisol is elevated, your body burns more protein as fuel through a process called gluconeogenesis, a process the liver uses to produce glucose from amino acids. As a result, you break down lean body mass to use the amino acids as fuel. In a situation like this, you need more carbohydrates from healthy, fiber-rich sources to keep your body from cannibalizing muscle tissue to make glucose as well as more dietary protein. At the same time, reducing stress in your life and giving your body more rest and recovery time between workouts.

 We’re All a Little Different

As you can see, how you respond to a diet depends upon whether you’re metabolically healthy, hormonal balance, how “stressed out” you are, and individual genetics. Age is also a factor. With age, especially after menopause, insulin sensitivity decreases. In response, you may develop some of the metabolic issues that people who are metabolically unhealthy experience, especially if you don’t exercise. One indication that this is happening is a gradual accumulation of stubborn belly fat, especially around the waist, that won’t seem to budge. Usually, this means you need to do more resistance training, do shorter periods of high-intensity cardio rather than long periods of moderate-intensity exercise and eliminate processed carbs and high-glycemic carbs from your diet while satisfying your appetite with more protein. The goal is to increase insulin sensitivity and improve the way your body handles glucose.

Age, in general, affects how your body responds to diet. A person who’s younger has a higher metabolic rate and will likely lose weight faster than someone middle-aged or older. Gender is another factor. Men usually lose weight more quickly than women on any diet since they have more metabolically active muscle and a higher metabolic rate.

When constructing an eating plan, consider your activity level. The more active you are, the more your body can tolerate carbohydrates, especially if you’re metabolically healthy. If you do high-intensity exercise, you should consume healthy carbs along with protein before a workout.

 The Bottom Line?

Now you know why some people respond better to a particular diet and lose more weight than someone else – even when eating the same things. Keep in mind that what’s optimal for your body can change over time. You need more carbohydrates during periods when you’re exercising hard, but fewer as you age. You may discover the macronutrient composition of the diet you ate at age 20 no longer works at age 50. Time to make adjustments! You may need to increase the amount of protein in your diet, lower the carb content of your diet and choose more fiber-rich carbohydrate sources.  All in all, you can’t go wrong at any age choosing fiber-rich carbs, fruits and vegetables, whole grains in place of refined ones, lean protein sources, fatty fish and healthy sources of fat.



On Fitness. January/February 2015. “Fat War Strategies”

Obes Res. 2005 Apr;13(4):703-9.

Today’s Dietitian. Vol. 15 No. 7 P. 42. June 2013.


Related Articles By Cathe:

5 Reasons to Ditch Restrictive Dieting

Why There Is No “Best” Diet

Do Low-Fat Diets Impede Weight Loss?

Does Meal Frequency Have an Impact on Body Composition?

Is There an Ideal Macronutrient Ratio for Fat Loss?


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