Jeff S. Volek

“Feeling Faint Issue: I’m happy losing weight with a low carbohydrate diet, but I’m always tired, get light headed when I stand up, and if I exercise for more than 10 minutes I feel like I’m going to pass out. Response: Congratulations on your weight loss success, and with just a small adjustment to your diet, you can say goodbye to your weakness and fatigue. The solution is salt…a bit more salt to be specific. This may sound like we’re crazy when many experts argue that we should all eat less salt, however these are the same experts who tell us that eating lots of carbohydrates and sugar is OK. But what they don’t tell you is that your body functions very differently when you are keto-adapted. When you restrict carbs for a week or two, your kidneys switch from retaining salt to rapidly excreting it, along with a fair amount of stored water. This salt and water loss explains why many people experience rapid weight loss in the first couple of weeks on a low carbohydrate diet. Ridding your body of this excess salt and water is a good thing, but only up to a point. After that, if you don’t replace some of the ongoing sodium excretion, the associated water loss can compromise your circulation The end result is lightheadedness when you stand up quickly or fatigue if you exercise enough to get ‘warmed up’. Other common side effects of carbohydrate restriction that go away with a pinch of added salt include headache and constipation; and over the long term it also helps the body maintain its muscles. The best solution is to include 1 or 2 cups of bouillon or broth in your daily schedule. This adds only 1-2 grams of sodium to your daily intake, and your ketoadapted metabolism insures that you pass it right on through within a matter of hours (allaying any fears you might have of salt buildup in your system). This rapid clearance also means that on days that you exercise, take one dose of broth or bouillon within the hour before you start.”
― Jeff S. Volek, The Art and Science of Low Carbohydrate Living: An Expert Guide to Making the Life-Saving Benefits of Carbohydrate Restriction Sustainable and Enjoyable

“So let’s consider an alternative diet, say 1200 kcal consisting of 30% protein, 15% carbs (i.e., 180 kcal or 45 grams), and 55% fat. After a week or two of getting adapted (during which you may experience some of the fuel limitation symptoms discussed above), your serum ketones rise up in the range (1-2 millimolar) where they meet at least half of the brain’s fuel supply. Now if you go for that 5 mile run, almost all of your body’s muscle fuel comes from fat, leaving your dietary carb intake plus gluconeogenesis from protein to meet the minor fraction of your brain’s energy need not provided from ketones. And, oh yes, after your run while on the low carb diet, your ketone levels actually go up a bit (not dangerously so), further improving fuel flow to your brain. So what does this mean for the rest of us who are not compulsive runners? Well, this illustrates that the keto-adapted state allows your body more flexibility in meeting its critical organ energy needs than a ‘balanced’ but energy-restricted diet. And in particular, this also means that your brain is a “carbohydrate dependent organ” (as claimed by the USDA Dietary Guidelines Advisory Committee as noted in Chapter 3) ONLY when you are eating a high carbohydrate diet. When carbohydrate is restricted as in the example above, your body’s appropriate production of ketones frees the brain from this supposed state of ‘carbohydrate dependency’. And because exercise stimulates ketone production, your brain’s fuel supply is better supported during and after intense exercise when on a low carbohydrate diet than when your carbohydrate intake is high (see below).”
― Jeff S. Volek, The Art and Science of Low Carbohydrate Living: An Expert Guide to Making the Life-Saving Benefits of Carbohydrate Restriction Sustainable and Enjoyable