DEAR DR. BLONZ: I want to lose weight without a prescription drug. I am seeking information on fat-burning foods or supplements that are promoted for a claimed ability to help weight loss by making the body burn fat while you sleep. What about caffeine and herbal stimulants (not taken at night, of course)? Thank you in advance for your help. -- G.E., Raleigh, North Carolina

DEAR G.E.: There is no evidence of a meaningful increase in fat loss during sleep from adding specific foods. The "fat-burning food" label is mostly nonsense. Diet and sleep do interact, but the main levers are when and how much you eat, not magic nighttime foods.

Fat is metabolized (burned) as part of normal energy metabolism. To burn more, we must expend more energy, for example, through exercise and other forms of muscular work.

It is best to avoid turning to "stimulant" supplements, such as caffeine or guarana, for weight loss. The body needs rest to repair, regenerate and clear metabolic waste. It produces substances that promote rest when this is the case. The key calming substance is adenosine. Receptors on cell membranes respond to adenosine's presence by activating our metabolic brakes. Caffeine can bind to adenosine receptors and prevent the slowdown. While caffeine is thought of as a stimulant, it does not stimulate so much as it blocks the action of receptors that slow things down.

A reasonable intervention for weight loss without drugs is healthy eating combined with regular physical activity. Exercise not only burns calories, but it can also increase muscle mass, which has the added benefit of making the body burn more calories than other tissues, even at rest.

Regarding sleep, we all lose weight while resting. The only time we are not losing is when we are eating and drinking. The longest "fast" of the day is -- you guessed it -- when we are asleep! (Also, that's why the morning meal is named "breakfast" -- we "break" the "fast.") The idea, however, that a supplement will help you to drop a few sizes while you slumber is pure folly. For more on herbal remedies and weight loss supplements, see b.link/4vdmugu.

DEAR DR. BLONZ: What controls how much cholesterol the body manufactures? Can it make more cholesterol than it gets from food? -- E.D., Ames, Iowa

DEAR E.D.: Cholesterol is an essential structural component of every cell in the body. Even if there was no cholesterol in your diet, your body would have to make it. In addition, cholesterol is a precursor for several hormones, including estrogen and testosterone. Most of the cholesterol is manufactured in the liver. When cholesterol is present in the foods we eat, the liver is programmed to make less. There are several genetic conditions in which the body produces more cholesterol than it needs. Referred to as familial hypercholesterolemia, they tend to be rare (for more on this see b.link/smgfxsp).

More common, however, is the condition in which the body receives an unbalanced diet that's heavy on the carbs and processed foods and light on the whole food fresh fruits, vegetables and high-fiber grains. This results in blood cholesterol levels that are way out of whack. For more on using diet to lower cholesterol, see b.link/ypvky3a.

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: I am in relatively good shape for one in their 50s, and I eat well. I walk and exercise regularly, but not as much as I did earlier in life. Like many others in my group, I am annoyed by the weight around my middle. I can't improve my diet much more, and am frustrated at the bulge. Nothing has really changed except the shape of my body?! Any advice you can offer on aging, calories, and specific exercises would be appreciated. -- T.T., San Jose, California

DEAR T.T.: With aging, there is a natural decline in the energy (calories) the human body requires. There is also a tendency to decrease activity. Both contribute to changes in body shape, especially with individuals who continue to consume the same (or more) amount of calories, particularly if more processed foods with added sugars have entered the mix. There is also the fact that our body weight is packed into a smaller frame due to age-related loss of height from reductions in bone mass and increased spinal compression. (For more on the effects of aging on body shape, see b.link/2a3d3ay.)

There are three basic elements to our daily caloric demand. First and foremost is the resting metabolic rate (RMR). This is energy needed to keep the body alive, but not to fuel activities. Consider this our "cost of living," which represents about 60% to 75% of the daily caloric requirement. Next is the energy used for physical activity. For an average individual, this is about 15% to 30% of the calories we need. Finally, we have the thermic effect of food (TEF), also called thermogenesis, the energy released as heat as we eat and digest food. TEF accounts for about 5% to 10% of our daily calories, and tends to be higher in those with regular exercise habits. (More on thermogenesis at b.link/gls72y2.)

Fewer calories are burned by an aging body than its younger version, even if eating and physical activity remain the same. This age-associated decline is not solely attributable to the loss of lean body mass (muscle, organ and bone) that accompanies aging.

Muscles burn calories even when you are lying around, so do your best to maintain your muscle mass to help slow any age-related decline. (Think of the difference between the gas burned by a 4-cylinder engine idling at a stop light versus an 8-cylinder doing the same.)

The cumulative effect of stress can also contribute to that unwanted midline bulge. The body reacts to stress by bringing fuels into the blood to prepare for action. This occurs even if the stress is psychological and won't require a physical response. Ephedrine (adrenaline) and norepinephrine are the stress hormones that increase fuel levels. Cortisol is the stress hormone that helps calm things down and return blood fats to storage. Receptors in the abdominal area are more sensitive to cortisol, which can lead to greater fat accumulation in that area when stress is habitual.

Keep up with your activities. There should be elements of both aerobic workouts and resistance exercises to maintain your muscle mass. Consider speaking with a trainer to see if there are specific exercises to help with muscle tone in problem areas. Working on your core muscles is particularly helpful as it supports the back, another aging-associated issue we want to stay ahead of.

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: How risky is it to drink orange juice that is a bit fizzy? Does the fizz indicate that oxygenation is occurring? Isn't this associated with the process that creates free radicals? I know that free radicals are harmful to our health, but I also know that we can't survive long without an adequate supply of oxygen to the brain. Oxygen is obviously indispensable for our survival, but are there times when it compromises our health, as in drinking fizzy orange juice? Thanks for any clarification. -- R.L., Raleigh, North Carolina

DEAR R.L.: First, a bit about fizz when done intentionally. The "fizz" in drinks comes from carbonation, where carbon dioxide (CO2) gas is added to water. Carbon dioxide does not dissolve well in water, but it becomes more soluble as the temperature decreases. Pressure can also be used to "hold" the gas in solution. If you like your fizz, consume your carbonated beverages when cold and recently uncapped. This is why there is a louder "pop" and greater release of gas when a soda is uncapped at room temperature. Carbon dioxide is only loosely held by water, which explains why agitation, such as pouring a warm soda over ice, or shaking the bottle at any temperature, triggers a gaseous eruption.

When you consume carbonated beverages, some of the swallowed gas is absorbed and exhaled. The rest exits through belching, a process in which the esophagus opens and allows the pent-up gas to escape from the stomach. If it manages to pass through the stomach, the remaining gas can then pass through the GI tract and exit at the other end.

An interesting take on this topic relates to beer. The "proper" way to consume this carbonated beverage is to pour it so the fizz escapes and forms a foamy head, not down the side of the glass to minimize the effect. Drinking beer this way helps prevent bloating and belching, and is associated with better flavors. For more on beer carbonation, see b.link/5rb2fae.

Back to orange juice: The fizz you noticed developing is a sign of spoilage due to microbial fermentation of the juice's sugars. It is not a sign of free radical oxidation or oxygen. The fermenting organism gives off carbon dioxide gas that can be detected on your tongue, thus giving a sensation similar to that caused by carbonation. The organisms consume glucose, which results in that loss of sweetness. The fact that the orange juice in your example still tasted sweet might make it seem as though only a limited amount of fermentation had occurred. But, because the spoilage organism is unknown, it is best to discard any beverage or food that has become unexpectedly carbonated.

Send questions to: "On Nutrition," Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.