The Lowdown on Low Carb Diets
The Lowdown on Low Carb Diets
Your Guide to Manipulating Fat Loss
Bodybuilders have long used carbohydrate depletion during the final days prior to competition to hone and sharpen their physique. As willing “guinea pigs,” it is easily realized they would experiment with an Atkins-type, low-carbohydrate diet as a means to deplete body fat. The Atkins diet is best known for the initial ketogenic phase, but its long-term success is due to a transition to a low-glycemic load maintenance phase. Though bodybuilders focus on the higher protein component of such diets, clinical and metabolic effects are often due to the combined presence of relatively high dietary fat and low carbohydrate content.
Initially, many people reveled in the rapid “cutting” effect of these diets. Natural bodybuilders were particularly pleased, as they were able to avoid the body's survival response of dropping the metabolic rate (calorie burning) and holding onto fat stores in the presence of a perceived period of starvation (hypocaloric dieting). Over time, a pattern began to emerge, even in drug-enhanced bodybuilders, of a depletion of muscle mass and fullness. As happens time and again, the cycle has completed and low-carbohydrate diets are used, but only periodically— not as a maintenance diet among bodybuilders and athletes. Instead, the trend has been to return to a balanced diet of approximately 40/40/20 carbohydrate/protein/fat ratio by calorie. This allows for strength and mass gains, as well as a presentation of fullness and definition if the calorie intake is controlled.
In regards to health and weight loss, low-carbohydrate/high-fat diets (LCHF) have been shown to be more rapid, and at least equally effective as traditional diets (e.g., low fat, Ornish, Zone, etc).1,2 Though there is considerable controversy (no surprise given the revenue generated in the weight-loss industry), after initial concerns about increased cardiovascular risk, later evidence showed net beneficial cardiovascular changes in cholesterol and triglycerides in blood tests.2 To date, no study has shown any diet to provide a long-term reduction in chronic disease or mortality (premature death) risks. However, given the ability of protein to aid in satiety (fullness), and the previously accepted but now controversial association between calorie restriction and longevity (e.g., traditional diet of Okinawa), some of the benefits may be related to better adherence or lower calorie intake, as well as improved insulin sensitivity.3 Note, calorie-restricted diets are associated with lower testosterone in males.4
Though its popularity has waned, LCHF diets remain in the public conscious and on the bookshelf. Overwhelmed recently by the re-emergence of the human chorionic gonadotropin (hCG) diet, which is has not been proven to be more than a very low-calorie diet (VLCD) restricting subjects to 500 calories per day, LCHF diets are still a common “six-week solution” for brides, bodybuilders and beach destination vacationers. This certainly warrants a review of recent findings relating to LCHF diets, particularly for those who might choose to embrace this as a long-term lifestyle.
Cardiovascular Health
As stated earlier, LCHF diets may improve some of the risks factors associated with cardiovascular disease, namely cholesterol and triglyceride.2 The general public may be forgiven for believing this defines the absolute value of this type of diet on cardiovascular health. Unfortunately, it is much more complicated. Among the factors that determine a person’s propensity towards an adverse cardiovascular event (risk of harm) is small vessel reactivity. In other words, if the tissue needs more oxygen or there is too much pressure coming into the vessel, will it dilate? Much like a water hose, arteries manage pressure by widening or narrowing, similar to opening or closing the garden-hose nozzle when you wash your car. Several studies have noted that LCHF diets affect small vessel reactivity negatively, making the arteries less responsive to signals that pressure is too high or the tissue needs greater blood flow.5,6 While the normal, healthy person may not feel the difference, people at risk of ischemic events (e.g., heart attack, peripheral artery disease) may experience more frequent or severe symptoms; this may be particularly true for those with visceral obesity and/or type 2 diabetes mellitus. It is unknown if people with Raynaud’s disease might be affected.
Insulin Sensitivity in LCHF
Visceral fat is fat that collects around the organs inside the abdomen. When it exceeds a safe mass, inflammatory molecules and harmful metabolic hormones create changes that lead to insulin resistance, liver dysfunction, vascular changes and other negative effects. Weight loss of 5 percent or greater, regardless of diet or exercise used to achieve this, improves insulin sensitivity and other metabolic measures.8 Insulin acts on fat cells to suppress (reduce) the breakdown and release of stored fat, and promotes the uptake and storage of fatty acids from the blood. Muscle cells are also insulin sensitive, activating the uptake of glucose (sugar) from the blood, and suppressing the breakdown of cellular proteins— called the anti-catabolic effect. As a person becomes more insulin resistant, fat cells become hypertrophic (large); muscle cells also become less responsive to insulin’s signal. If obesity exceeds a certain point, this becomes a pathologic cycle. The fat cells do not suppress the breakdown of stored fat; this leads to a chronically elevated free fatty acid concentration in the blood. When this occurs, the fat deposits elsewhere (liver, muscle cells), increasing the insulin resistance of these tissues, and suppresses the release of growth hormone.
One would think that LCHF diets may be the best choice in this situation, as they lower insulin and lead to a more rapid weight loss. In fact, it may be best to lose weight first using a more balanced diet (e.g., Zone Diet), as a study in human subjects shows that at the level of the muscle cell, insulin sensitivity is improved with HIGH carbohydrate/LOW fat diet and worsened with LCHF diets.9 For the exercising dieter or bodybuilder, this might explain the continued muscle atrophy or impaired hypertrophy suggested to be present with LCHF.
Rapid Results, But Take Caution
LCHF diets are rapid, effective and appear to be well-tolerated (safe) in healthy, active people. However, those with type 2 diabetes, visceral obesity or a history of cardiovascular disease may be better served to follow a more balanced diet until their health improves. Obesity is not just a cosmetic issue; it can be a health threat. Those who are suffering negative health effects from obesity should heed the oft-ignored advice to “consult your physician before beginning a diet or exercise program.”