Tag: Caloric Restriction

How Much Exercise Do You Need to Lose Weight?

On By Dr. Scott RennieIn Weight Loss & Metabolic HealthLeave a comment

Patients ask me all the time how much exercise really matters for weight loss. The honest answer is that it depends on what they are trying to do. Losing weight quickly, keeping it off, and staying healthy are three different goals, and exercise performs very differently against each one.

On one point the research is not ambiguous. Exercise on its own rarely produces large weight loss. Most trials show modest changes, roughly half a kilogram to three kilograms, and that is in people putting in 180 to 270 minutes a week (Jakicic et al., 2019). Below 150 minutes, most people do not lose much at all. I see the same thing on my schedule. Patients who start walking three times a week often feel noticeably better while the scale barely moves, and that gap is worth naming out loud before they get discouraged by it.

None of which makes exercise optional. It is among the best tools we have for preventing regain. Long-term data show that people sustaining higher volumes, often north of 250 minutes a week, are considerably more likely to hold onto a 10 percent loss (Jakicic et al., 2014). That is where the real return sits.

Paired with dietary change, the numbers improve. Adding exercise to calorie restriction increases short-term loss by about 20 to 25 percent over diet alone (Wing et al., 1998; Goodpaster et al., 2010). I had a patient who was cutting calories carefully and getting almost nothing for it until she added regular cycling. With both together she lost roughly twice as much and held it considerably longer.

Type and volume both matter. For general health, 150 minutes of moderate activity a week is the baseline. For meaningful weight loss, 250 to 300 minutes is closer to what is needed. For maintenance, somewhere in the 200 to 300 range seems to work. None of this requires a gym. Walking, yard work, and even light activity like standing or slow walking accumulate, and a 2021 doctoral dissertation found that increasing light-intensity activity independently predicted weight loss at both 6 and 12 months (Jackson, 2021).

Practically, I tell patients to start from where they actually are. Adding steps, breaking up long stretches of sitting, and picking something they do not dread produces more consistency than any prescribed routine they will abandon in a month. Thirty to sixty minutes on most days works whether it comes in one block or four. And if weight loss is the goal, it has to be paired with dietary change; exercise alone will disappoint them.

Exercise is not a shortcut to weight loss, and patients who come in expecting it to be will be let down. What it does do is keep lost weight off, improve metabolic health, and protect function as people age. Move more, sit less, keep going.

Scott Rennie, D.O.

References

Jakicic JM et al. Physical Activity and the Prevention of Weight Gain in Adults: A Systematic Review. Med Sci Sports Exerc. 2019;51(6):1262-1269.

Jakicic JM et al. Obesity. 2014;22:2284-2292.

Goodpaster BH et al. JAMA. 2010;304(16):1795-1802.

Wing RR et al. Am J Clin Nutr. 1998;67(3):551-558.

Physical Activity Guidelines Advisory Committee. 2018 Scientific Report.

Jackson R. Doctoral dissertation, 2021.

Board Certified in Obesity Medicine and Family Medicine

This blog is for educational purposes only and does not constitute individual medical advice. Always consult your own physician before making changes to your health, medications, or treatment plan.

Does Fasting Slow Aging? What the Science Says

On By Dr. Scott RennieIn Longevity & Healthy AgingLeave a comment

Aging cannot be stopped. The pace of it may be influenced by what and when we eat, and that idea is old rather than new. Since the 1930s, animal studies have shown that cutting calories without causing malnutrition extends lifespan. Rodents held at a 30 percent reduction lived longer with less cancer and less heart disease.

The proposed mechanisms are lower oxidative stress, better mitochondrial function, and less inflammation. Less fuel in, less metabolic wear.

Then you move from mice to people and it gets complicated.

The CALERIE trials brought calorie restriction into human research. CALERIE II found that cutting roughly 15 percent of calories for two years improved blood pressure, cholesterol, and markers of oxidative stress, and those benefits appeared without major weight loss (Kraus et al., 2019). The obstacle is adherence. Sustained restriction is hard on mood, on social life, and on nutritional balance, and most people will not hold it.

Which is how fasting patterns entered the conversation. Intermittent fasting covers several approaches. Some people fast on alternate days. Others follow 5:2, eating normally five days a week and restricting on two. Time-restricted feeding, which confines eating to an 8 to 10 hour window, has drawn the most recent attention.

Alternate-day fasting does produce fat and weight loss, but hunger is a serious barrier and dropout rates run high. Modified versions have not clearly outperformed standard calorie restriction (Trepanowski et al., 2017).

Time-restricted feeding looks more workable. Sutton and colleagues tested an early schedule with all meals between 7 a.m. and 3 p.m. Participants did not lose weight, but insulin sensitivity, blood pressure, and oxidative stress markers all improved, and they reported less hunger through the evening (Sutton et al., 2018). Other short-term work points the same direction, particularly on appetite control and metabolic flexibility (Hatori et al., 2012; Varady et al., 2022).

What does that mean in practice? Calorie restriction has the strongest animal data and some genuinely promising human results, and almost nobody sustains it. Alternate-day fasting rarely survives contact with real life. Time-restricted feeding is the one most patients can actually keep, and even moving to a 10 hour window and dropping late-night meals is a defensible starting point.

When I talk this through with patients, I usually suggest starting at a 12 hour window and tightening it only if they tolerate the change well. What goes in the window still matters more than the window does, and nutrient density should not get lost in the enthusiasm about timing.

Fasting is one tool among several, and which one fits depends on the person, their health, and what they can hold onto for longer than a month.

Scott Rennie, D.O.

References

Ravussin E, Redman LM et al. 2015.

Kraus WE et al. Lancet Diabetes Endocrinol. 2019.

Sutton EF et al. Cell Metab. 2018.

Trepanowski JF et al. JAMA Intern Med. 2017.

Heilbronn LK et al. 2005.

Spadaro PA et al. 2022.

Hatori M et al. Cell Metab. 2012.

Varady KA et al. 2022.

Board Certified in Obesity Medicine and Family Medicine

This blog is for educational purposes only and does not constitute individual medical advice. Always consult your own physician before making changes to your health, medications, or treatment plan.