Glucosamine and chondroitin during a cut: does it help

A cut is a period when calories drop, cardio increases, and the joints and ligaments often start to "remind you they exist." It is exactly then that many athletes think of glucosamine and chondroitin. The editorial team looked into what these supplements can and cannot do under conditions of an energy deficit, and whether it is worth spending on them a budget that during a cut is usually already tight.

Why joints suffer specifically during a cut

During a cut, the load on the musculoskeletal system changes on several fronts at once. The share of cardio grows — running, incline treadmill walking, the stepper — and the knee and ankle joints receive thousands of extra repetitive cycles per week. For those who previously barely ran, this is a sharp jump in volume, to which connective tissue adapts much more slowly than muscle.

The second reason is the energy deficit itself. When calories are lacking, the body conserves resources, and the repair of slow-turnover tissues, in particular tendons and cartilage, may slow down. The IOC consensus on relative energy deficiency in sport (RED-S) describes that prolonged energy shortage is linked to poorer bone tissue status and a higher risk of injury.

The third factor is fatigue. Toward the end of a cut, exercise technique often "falls apart": concentration drops, there is less strength, yet the athlete tries to hold the working weights. It is at such moments that overloads of the elbows, shoulders and knees appear, which are subjectively perceived as "the joints started to hurt from the diet."

Finally, some athletes sharply cut fats from the diet. This in itself does not destroy the joints, but together with low calories and high training volume it creates a feeling of overall "dryness" and discomfort that people try to compensate for with supplements.

What glucosamine and chondroitin actually do

Glucosamine is an amino sugar, one of the building blocks of the glycosaminoglycans of cartilage. Chondroitin sulfate is a large polysaccharide that is itself part of the cartilage matrix and is responsible for its ability to retain water. The idea behind the supplements is simple: give the joint "raw material." The problem is that the body synthesizes these substances on its own, and delivery of an oral product specifically to the cartilage is not as direct as advertising promises.

The main evidence base concerns not athletes but people with osteoarthritis of the knee or hip joint. The best-known study, GAIT (Clegg et al., 2006), in over 1,500 patients, showed no advantage of glucosamine, chondroitin or their combination over placebo for the whole sample; a certain signal was observed only in the subgroup with moderate to severe pain.

The network meta-analysis by Wandel and co-authors (2010) in the BMJ concluded that these supplements provide no clinically meaningful effect on joint pain compared with placebo. At the same time, individual studies with crystalline glucosamine sulfate (Reginster et al., 2001) reported a slowing of joint-space narrowing with long-term use.

For healthy trained people without a diagnosis there is little data. There is a small study by Ostojic and co-authors (2007) on glucosamine after acute knee injury in athletes, but it gives no grounds to speak of "prevention" of injuries. The IOC consensus on dietary supplements (Maughan et al., 2018) does not include these substances among supplements with proven benefit for athletes.

Do they affect fat burning and glucose

The short answer is no. Neither glucosamine nor chondroitin has a mechanism that would accelerate lipolysis, increase energy expenditure or suppress appetite. If promises of "weight-loss support" appear on the label of a joint complex, that is marketing, not pharmacology.

The question that really arises in people on a diet is whether glucosamine interferes with blood sugar control, since it is a glucose derivative. In laboratory models, intravenous administration of large doses of glucosamine worsened insulin sensitivity, which at one time caused concern. However, the review by Simon and co-authors (2011) on oral intake at usual doses found no clinically meaningful effect on glucose in people without diabetes.

The caloric content of a daily serving of such supplements is negligible and does not affect energy balance. Still, it is worth paying attention to the dosage form: effervescent tablets, flavored powders and "chewable" forms may contain sugar or sweeteners. During a cut this is a trifle, but together with other "invisible" calories it is worth taking into account.

For people with diabetes or prediabetes who monitor their glycemia, the editorial team advises discussing any new supplements with a doctor and tracking indicators after starting them, rather than relying on the general conclusions of reviews.

For whom during a cut they may be appropriate

If an athlete already has confirmed degenerative joint changes or a doctor has diagnosed early osteoarthritis, the supplement may be part of a broader strategy — alongside load correction and physiotherapy. The European ESCEO algorithm (Bruyère et al., 2019) permits prescription crystalline glucosamine sulfate and pharmaceutical chondroitin as an option for the baseline therapy of knee osteoarthritis.

In contrast, the American ACR guidelines (Kolasinski et al., 2020) and the OARSI recommendations (Bannuru et al., 2019) do not recommend glucosamine and chondroitin for knee osteoarthritis. Such disagreement between authoritative organizations in itself indicates that the effect, if there is one, is small and depends on product quality.

For all other scenarios it is reasonable to honestly acknowledge: this is a self-experiment with a low probability of a noticeable result. If a person still wants to try, studies usually used 1,500 mg of glucosamine and 800–1,200 mg of chondroitin per day, and the effect was assessed no earlier than after a few weeks.

It is important not to confuse the effect of the supplement with weight loss as such. Losing each kilogram of body mass reduces the mechanical load on the knees during walking, so improved joint well-being at the end of a successful cut is often linked precisely to this.

What matters more than joint supplements in a deficit

First — managing cardio volume. Instead of a sharp switch to daily running, it is better to add activity gradually and alternate impact types with non-impact ones: stationary bike, elliptical, swimming, walking. This reduces the repetitive load on the same structures.

Second — protein and total energy. Too aggressive a deficit harms not only muscle but also connective tissue. A moderate rate of weight loss and adequate protein intake help preserve the body's recovery resources.

• Gradualness:increase cardio volume not in jumps but in steps, with weeks of adaptation.
• Technique:toward the end of a cut it is better to reduce the working weight than to "grind it out" with poor technique.
• Sleep:lack of sleep heightens the perception of pain and slows recovery.
• Body signals:swelling, night pain, joint instability are a reason to see a doctor, not to buy a new jar of supplements.

Third — deload weeks. During a cut the temptation to train without breaks is great, but a planned reduction of volume once every few weeks often does more for the joints than any supplement.

And finally, if pain persists for more than two to three weeks despite load correction, it is worth getting examined. Chronic pain in the knee or shoulder may be a sign of tendinopathy or a meniscus injury, which require a different approach.

Editorial conclusions

Glucosamine and chondroitin do not help burn fat and have no proven protective effect for the healthy joints of an athlete during a cut. Their evidence base concerns mainly osteoarthritis, and even there expert organizations diverge in their assessments.

The effect of glucosamine on glucose levels with oral intake at usual doses is, according to available data, clinically insignificant, so for a healthy person on a diet this supplement poses no problem, but no benefit should be expected from it either.

Joints during a cut are better protected by a gradual buildup of cardio, a moderate deficit, good technique and deloads. It makes sense to consider the supplement only for specific indications and together with a doctor.

We also recommend reading our materials on the myths about glucosamine and chondroitin, on the difference between glucosamine and MSM, and on how to choose a quality product by its label.

References

1. Clegg DO, Reda DJ, Harris CL, et al. Glucosamine, chondroitin sulfate, and the two in combination for painful knee osteoarthritis. N Engl J Med. 2006;354(8):795–808.
2. Wandel S, Jüni P, Tendal B, et al. Effects of glucosamine, chondroitin, or placebo in patients with osteoarthritis of hip or knee: network meta-analysis. BMJ. 2010;341:c4675.
3. Reginster JY, Deroisy R, Rovati LC, et al. Long-term effects of glucosamine sulphate on osteoarthritis progression: a randomised, placebo-controlled clinical trial. Lancet. 2001;357(9252):251–256.
4. Simon RR, Marks V, Leeds AR, Anderson JW. A comprehensive review of oral glucosamine use and effects on glucose metabolism in normal and diabetic individuals. Diabetes Metab Res Rev. 2011;27(1):14–27.
5. Bruyère O, Honvo G, Veronese N, et al. An updated algorithm recommendation for the management of knee osteoarthritis from the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO). Semin Arthritis Rheum. 2019;49(3):337–350.
6. Kolasinski SL, Neogi T, Hochberg MC, et al. 2019 American College of Rheumatology/Arthritis Foundation guideline for the management of osteoarthritis of the hand, hip, and knee. Arthritis Rheumatol. 2020;72(2):220–233.
7. Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439–455.
8. Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). Br J Sports Med. 2023;57(17):1073–1097.