The Right Way To Diet To Lose Fat And Maintain Muscle

By Dan Gwartney, MD

What is the best way to lose weight? The correct answer is whatever works best for the individual. Of course, there is no ‘one size fits all’ diet, as there are people who have unique metabolic or genetic traits that predispose them to respond differently from the rest of the human herd.

It is impossible to directly compare every diet. However, in looking at the generalities of the various diets, one sees trends. In the United States, many health agencies still advocate a low-fat approach. During the 1990s, two ‘revolutionary’ diets took the market by storm – The Zone and Atkins. These diets were decried as ineffective and dangerous by dietitians and cardiologists. Yet, study after study reported that these diets were at least as effective as low-fat diets – often, more so.1-4 Further, health benefits were reported – including cardiovascular benefits – despite increased dietary fat intake.

The Right Way To Diet To Lose Fat And Maintain Muscle


Weight trainers, fitness enthusiasts and image-minded people alike flocked toward the low-carb options due in part to the novelty, as well as the publicity created by the controversy. The number of people following the ‘low-carb craze’ was so great that it threatened the financial solvency of stock market darlings such as Krispy Kreme. A few longer-term, direct comparative studies have shown that while people tend to lose more weight quickly with the Atkins diet, over the course of a year, the diets produce comparable weight-loss results.1-3

For the performance-minded person, weight loss is secondary to fat loss. Further, the loss of muscle mass, strength or drive can be considered a strong detriment. Great care must be taken in selecting the proper training and diet regimen when attempting to cut up (get leaner).

Professional weightlifters and fitness models learned long ago that eating sweets is one of the easiest ways to sabotage fat loss. Most athletes adapted a common-sense practice of eating non-processed carbohydrates (rice, baked potatoes and whole-grain oats) and never ate a meal that did not include a substantial amount of protein in the form of meat or eggs. One difficulty faced by many athletes was keeping calories down, as these meals tended to result in a daily consumption above maintenance requirements. The introduction of protein powders provided a less expensive and more convenient means of consuming a greater percentage of calories as protein, without the caloric burden of fat. Suddenly, it became possible for the informed consumer to manipulate the macronutrient ratio of his diet however he pleased.

This led to years of experimentation as people experimented with a variety of diets, from low-fat, to ‘balanced’ to low-carb to ketogenic. In agreement with the clinical trials, low-carb and ketogenic diets resulted in rapid and significant weight loss. Not only was the scale showing progress, but skin tightening and vascularity became prominent more quickly and easily. Early adapters continued to push the limits of carb depletion, embracing ketogenic diets.

Ketogenic diets are extremely low-carb diets— less than 20 grams per day— that force the body to rely on fatty acid oxidation (fat calorie burning) and protein catabolism (breaking down protein) to meet the body’s energy needs.5-7 If a sufficient amount of protein and fat is consumed throughout the day, much of the muscle mass can be maintained while dramatic fat loss occurs.8

While low-carb and ketogenic diets are ideal for sheer fat loss, this does not necessarily mean they are optimal for the specific population of athletes or those with physique-building goals. It is also important to account for the metabolism-altering effect of drugs when considering diet advice being discussed, especially on message boards or websites that promote such use. When anabolic steroids, growth hormone, insulin, thyroid hormone(s), other growth factors and lipolytic (fat-burning) drugs are used, the rules go out the window.


Muscularity, muscle function and alertness/drive are all affected negatively by extremely low-carb diets. Briefly, muscularity depends on inflated muscle size and fullness as much as it does on stripping the overlying subcutaneous (under the skin) fat. Undoubtedly, the maximal amount of subcutaneous fat loss will occur in ketogenic conditions. However, the same conditions impair the muscle tissue’s ability to maintain turgor (fullness), develop a ‘pump’ and retain the level of development attained with a more balanced diet.

Low-carb intake stresses the body, particularly the liver and skeletal muscle. Short-term and high-intensity exercise is dependent on immediate fuel sources, glucose (sugar) and phosphocreatine.9 Creatine is maintained at a fairly constant concentration in muscle as it is ‘recycled,’ though it can be increased to a degree with supplementation.10 Sugar availability varies to a much greater extent as it is actually used up.

Sugar is stored in the muscle and liver as glycogen, a branched-chain of numerous glucose molecules hooked together. With prolonged exercise during a low-carb diet, the glycogen stores are used up; this forces muscle to rely more heavily on fatty acids.11, 12 As more fatty acids are shuttled through the mitochondria, the rate of uncoupling increases to reduce oxidative stress.13 Uncoupling describes disconnecting energy production from calorie burning. This is a ‘positive’ in terms of fat loss, but decreases the ability of the muscle to recover from exercise.

Proteins in the muscle are also broken down to create a pool of amino acids that can pass through the energy-producing cycle.14, 15 These amino acid-based compounds are called ketone bodies. Other amino acids are released into the bloodstream, traveling to the liver to be converted into sugar through a process called gluconeogenesis. Unchecked, this process progressively breaks down muscle. How is the catabolic effect of exercise held in check? By providing the proper nutrients, especially in the first several minutes following exercise. Protein, especially the amino acid leucine, activates anabolic (rebuilding) pathways and suppresses catabolic (breakdown) pathways.16

Of course, there is plenty of leucine present in low-carb diets. The greatest benefit post-exercise occurs when a moderate insulin surge is released when simple carbs are ingested. This insulin surge occurs in two phases. The first spike shuts down gluconeogenesis, followed by a second wave that stimulates glucose uptake into insulin-sensitive cells, including the liver and skeletal muscle.17 Insulin also initiates a cascade of reactions in skeletal muscle tissue that rapidly and potently suppresses proteolytic breakdown of the structural and contractile proteins in muscle.17-19 Additionally, glycogen storage is promoted in muscle and the liver, replenishing the tissues and preparing the body for later exercise.20


Low-carb diets, especially ketogenic diets, do not provide substantial insulin surges. While this is a great benefit in terms of fat loss, it is a detriment in terms of long-term muscle function and growth. There is no established insulin pattern that is optimal for fat burning, as responses vary significantly among individuals. Even in the same person, cellular responses to insulin differ— from the ‘fed’ to the ‘fasted’ state, depending on intramuscular fat stores, etc.22 Diet gurus and athletes alike have found that it is much easier to control insulin (and the accompanying storage of water and fat) by eating smaller meals more frequently, with preference toward foods with a low glycemic index. Only the meal immediately following exercise should contain a high glycemic-index carb source.

Another drawback to extremely low-carb diets is the persistence of hypoglycemia (low blood sugar).23 When the body senses that the circulating blood concentration of glucose (sugar) is low, counter-regulatory mechanisms are activated. This is actually a complex scheme, but a basic understanding offers some insight as to why this is counter-productive to building or maintaining muscle mass.

The response to hypoglycemia is many fold. Most of the actions occur through the influence of counter-insulin hormones (hormones that produce the opposite results as insulin). The most immediate and potent of these hormones is neurochemical norepinephrine and the related hormone, epinephrine (adrenalin).24 Think of a time when you may have experienced hypoglycemia, perhaps after a day when your schedule forced you to skip several meals. While your mind may have felt sluggish, and perhaps you were fatigued, did you notice your heart racing or a tremor in your hands?

When faced with hypoglycemia, the body releases these potent stimulating chemicals from nerve endings and the adrenal medulla (a gland located near the kidneys) that jolts your body like a double dose of espresso. Other hormones are released, and the net sum of these reactions is to shove the gluconeogenic and lipolytic reactions into overdrive to provide more available energy from body stores in the (perceived) absence of food. However, this is a double-edged sword, as norepinephrine, adrenalin and cortisol feed the body by robbing the liver and muscle of protein at the same time that fat cells are dumping stored body fat. Nobody gets lean through starvation, they just get smaller. Unfortunately, the body judges starvation, to a large degree, by the amount of available glucose. There is some compensation as growth hormone is also a counter-insulin hormone, but growth hormone has very little anabolic function in a catabolic environment.


The absolute number of carb grams that should be consumed daily is difficult to ascertain, and only general guidelines can be given due to the broad range of bodyweight, composition, activity, age, etc. If fat loss without sacrificing lean mass is the goal, carbohydrates should be limited, but not excluded. A couple of guidelines:

  • No meal should contain more than 30-40 grams of carbohydrates, and aside from the post-workout meal, fewer than 10-12 grams of simple sugars.
  • Total daily intake should be limited to between 50-200 grams of carbs; the number will need to be adjusted, based on individual response.

I am working on a hypothesis that the optimal carbohydrate intake is equal to the caloric demands of activity, not maintenance calories. This is similar to the carbohydrate threshold mentioned by researcher Layne Nortonbelow 50 grams of carbs, people begin to have difficulty with power movements, recovery, alertness, cognitive processing, etc. Below 20 grams of carbs, physical, mental and social function is noticeably impaired, though some people adjust to the diet and do quite well. Again, there are no absolutes when it comes to dealing with people.

In the broadest view, food consists of carbohydrates, protein and fats. It has already been stated that carbohydrates should be present in sufficient amount to support lean mass and avoid the catabolic effect of hypoglycemia, but not in excess to avoid the fat-storing promotion and fat-loss suppressive effects of high insulin spikes. Slowly releasing carbs throughout the day, added to a quick-releasing carb source immediately post-workout, should allow for this if the total carb intake is controlled.


Dietary protein is the source of amino acids that provides the structural and functional components of muscle tissue. In a setting with sufficient insulin, protein needs are less as insulin has a potent protein-sparing effect.25 This is due in large part to insulin’s ability to stop the breakdown of proteins in muscle, as well as shutting down the gluconeogenic function of the liver, which converts amino acids robbed from muscle into glucose (sugar) to feed the rest of the body.

Protein is not just a building block, though. Consuming protein stimulates the release of many hormones, and certain small peptides and amino acids act as hormone-like substances. In fact, eating protein also stimulates the release of insulin.26 As with carbs, different proteins induce different insulin spikes. Among the best/worst, depending upon your perspective, are the ubiquitous (universally used) whey proteins.

One potential downfall to the insulinogenic effect of protein is the rebound hypoglycemia that would follow if the meal did not contain carbohydrates.26 To illustrate, consider a post-workout shake that is only whey protein and creatine. The body will release insulin in response to the sudden surge of amino acids rapidly absorbed from the drink, driving the amino acids and any sugar present in the bloodstream into the muscle, liver, etc. If blood glucose concentration was already low due to the metabolic demands of exercise, it falls even lower due to the protein-induced insulin surge. Consequently, the counter-insulin effect is even greater. Ironically, high-protein diets activate pathways that increase insulin resistance.27

Just as it is important to avoid consuming too great an amount of carbohydrate at once – and quickly absorbed carbs, except for post-workout – the same applies to protein. Whole food sources of protein are best during the remainder of the day, particularly as there are components in whole-food protein that are not present in protein powders – just as sugar doesn’t replace fruit. Fortunately, as long as large servings of quickly-absorbed proteins are not consumed, protein does not require a lot of thought. One caveat based on several years of observation is that soy proteins do not appear to support lean mass as well.28 Perhaps it is because soy is relatively deficient in the amino acid methionine, contains phytoestrogens and/or is plant-based.


Those hoping that fat might be simple will be disappointed. Advances in food technology were not limited to proteins and amino acids. Researchers learned to look beyond lard when studying dietary fat. ‘Fats’ are actually called triglycerides in chemical nomenclature, as they are composed of three different fatty acids that share a common glycerol molecule. The fatty acids are like three passengers sharing a ride in the same car (glycerol). When the fatty acids are hooked up to a glycerol, they are metabolically inert; this is the form they are stored as in fat cells. However, when the fatty acids are split off, they circulate as free fatty acids. Inside the cell, these fatty acids can be burned for energy. However, in the bloodstream, various fatty acids act as metabolic modifiers, appetite suppressants, anti-inflammatory agents, etc.

There are several fatty acid supplements on the market. Conjugated linoleic acid is marketed as a fat-loss aid, although conflicting results are present in the literature; there is also some controversy relating to an increased risk of increasing insulin resistance.29, 30 Oleoylethanolamide (OEA) is a fatty-acid amide that activates receptors in the gut and possibly on other tissues. OEA has been shown to reduce appetite and aid in weight loss and alleviate measures of depression.31 Using either or both of these fatty acids may be of benefit in losing fat, but that looks at fatty acids as a supplement.

Many diets encourage consumers to eat more fish. Certainly, there are many health benefits to adding fish to the menu, particularly those varieties that have high omega-3 content.32 Fish oils with omega-3 include the fats DHA and EPA. Both fish oil and fish protein have properties that accelerate fat loss and weight loss.33 Again, for the average dieter, these fats are an appropriate and wise component to add to the diet. However, for the select population of athletes and weight trainers, fish consumption may hold some unintended consequences.

Fish oil provides many of its health benefits by lowering inflammation.34 These omega-3 fatty acids interfere with the signaling cascade that begins with recruitment of inflammatory cells, release of cytokines (a class of hormone-like molecules) and secondary messengers.35 The state of obesity generates a high concentration of these inflammatory cytokines that impair metabolism, promoting further fat storage and damaging health. Insulin resistance, diabetes, cardiovascular disease and other health mishaps occur with much greater frequency as inflammation rises. By interfering with the inflammatory signaling of visceral adipose tissue and other fat stores, fish oils reduce whole-body inflammation.

Yet, like so many other pathways in the body, inflammation has a yin and a yang, or good effects as well as bad. Inflammation is a vital component of muscle growth.36-38 It sounds bizarre, but in order to experience the benefits of exercise, one need suffer the pain and swelling that accompanies microstructural damage. Ironically, many athletes sabotaged their training for years using anti-inflammatory medications such as aspirin and ibuprofen. Only recently has research reported on the blunting effect these drugs have on muscle growth and response to training. Recall that the health benefits of fish oils are due in large part to their anti-inflammatory properties. While no definitive clinical trials have been performed, animal and tissue studies support the hypothesis that a diet high in fish oil would impede muscle growth and training response.39-41 This may seem surprising, but there are many examples of healthy practices that are detrimental to physical performance.

When discussing the anti-anabolic effect of fish oil (and aspirin, ibuprofen, etc.), think back to one of the counter-regulatory responses during hypoglycemia (low blood sugar). Among the hormones released is cortisol. Cortisol is one of the most potent anti-inflammatory hormones in the human body. If cortisol levels are elevated due to persistently low blood sugar, it may impair the muscle’s ability to respond to exercise.42, 43 Of course, cortisol is also very catabolic (muscle wasting). Yet another reason to avoid ketogenic diets if muscle retention or gain is a priority during weight/fat loss.


In summary, there is no one perfect diet for everyone. In general, for people who seek to maintain or develop muscular strength or size, a diet that avoids persistent periods of hypoglycemia seems necessary to avoid the counter-productive responses that occur naturally to maintain blood sugar concentration high enough to nourish the brain and other vital organs. Additionally, one needs to remember that proteins can also induce an insulin response. If this occurs when blood sugar is already low and there are no carbs in the meal, then severe hypoglycemia can occur. While fats are generally viewed as nothing more than calories, an abundance of research has emerged, showing that the same benefits derived from omega-3 fatty acids in fish oil can blunt the anabolic effect of exercise, by reducing or blocking the microdamage-induced inflammatory response – much the same as aspirin and other anti-inflammatory medicines.

Athletes and fitness enthusiasts need to realize that they are not like everyone else. It is not enough to lose weight indiscriminately. The hard-earned muscle needs to be protected and nurtured or it will be lost along with any fat, resulting in reduced physical performance and lessening the aesthetic appeal when all is said and done. Some general rules are as follows:

  • Include a limited amount of carbs in a high-protein diet, avoiding any urge to go ketogenic. 50-200 grams of carbs is a ballpark range, working toward the low end if your metabolism allows.
  • Avoid large servings of whey, which induce a sharp insulin spike – except after training (possibly before as well if you split your meals that way)
  • Make sure to include some sugars along with the drink to avoid rebound hypoglycemia.
  • Non-soy, food-based protein sources are best. Not only will these provide slowly-digested protein, but also other essential nutrients that are a good source of arachidonic acid, an inflammatory fat.
  • Fish can be consumed in moderation, particularly if the diet is carbohydrate-poor
  • Do not supplement with fish oil as this may block the anabolic response of the muscle to exercise.
  • It is best to avoid using any aspirin-like drug.

Dieting and losing fat require a lot of sacrifice. Consider the points in this article as you design your diet, to avoid sabotaging your efforts and enjoy the benefits of working out smarter as well as working harder.


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